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Official sources are dead silent, and fan resources are no different—the franchise is experiencing clear stagnation... Practically all projects in the M&M universe have been wound down, some closed before even reaching release, and work on Heroes VII was halted shortly after the expansion's launch, leaving the game in a very raw state.
Is it worth expecting a continuation of the Heroes series in this situation?
What do we have at the moment? - A highly dubious rumor that Ubisoft's German division, Blue Byte, is developing a AAA strategy game in the RTS genre and that this project could be Might & Magic: Heroes VIII; here is the link:
https://www.tweaktown.com/news/57201/ubisoft-developing-new-aaa-pc-strategy-game/index.html
A question immediately arises: why Heroes 8 and RTS, when the latter has always been TBS? The article contains a link to a News item in UbiBlog
dated April 19, 2017,http://blog.ubi.com/ubisoft-expanding-europe-new-studios-opening-bordeaux-berlin/
which says the following:
"The team in Berlin will work closely with the BlueByte teams in both Düsseldorf and Mainz on an unannounced AAA project, and will help Ubisoft establish a presence in the German capital."
I saw no direct mentions of the platform or genre of the unannounced project there, other than: "Germany is home to Blue Byte, one of the most established names in German gaming and an industry leader in PC strategy games.", which can only be considered an indirect indication of the game's strategic genre and PC platform.
I checked what information was available on the Blue Byte website itself in my favorite section—vacancies...
Here, for example, is information from a game engine programmer vacancy:
https://www.bluebyte.com/en/career/vacancies#sr-post-id=743999660914438
"The newly established Ubisoft Berlin studio is set to continue contributing to this impressive line-up and will be working on AAA Co-Development projects together with international Ubisoft teams. The first project will be a big AAA-brand, one of the biggest and most important for Ubisoft."

Undoubtedly, the Might & Magic franchise fits the definition of one of the largest and perhaps most important for Ubisoft, but this is clearly not enough to draw conclusions.
There is also an application form on the Blue Byte website for those wishing to register as testers; in it, unfortunately, in the game preferences section, I saw no division between RTS and TBS, let alone any mention of Heroes. Along with other genres, it simply says: "Strategy (Star Craft, Civilization, XCOM…)", otherwise that would have been a huge spoiler. :)
It is quite possible that ANNO 1800 was hidden behind the unannounced project—which Blue Byte is currently working on and which was announced in August 2017 at Gamescom—but on the other hand, on October 18, 2017, already after the announcement of ANNO 1800, a post appeared on Facebook regarding a vacancy for a Community Strategist:
https://www.facebook.com/UbisoftBlueByteEN/photos/a.1040251262700174.1073741828.995469347178366/1623897734335521/?type=1&theater
The description of this vacancy on the site says the following: "Working with an exciting brand on an unannounced project, the position will be responsible for the strategic management of communities with a global focus."

Meaning that a certain unannounced project belonging to some exciting brand figures again, and they are looking for someone to work with the community... sounds painfully familiar, doesn't it? :D Could this project be Heroes 8? - It is impossible to say for sure yet, but there is potential.
P.S. How serious could all this be? - Time will tell.
For now, we can go back a bit into the past and compare it with the case when everything turned out to be serious:
http://www.might-and-magic.ru/blog/1/entry-3-might-and-magic-heroes-7-razrabatyvaetsya-v-limbic/
Is it worth expecting a continuation of the Heroes series in this situation?
What do we have at the moment? - A highly dubious rumor that Ubisoft's German division, Blue Byte, is developing a AAA strategy game in the RTS genre and that this project could be Might & Magic: Heroes VIII; here is the link:
https://www.tweaktown.com/news/57201/ubisoft-developing-new-aaa-pc-strategy-game/index.html
A question immediately arises: why Heroes 8 and RTS, when the latter has always been TBS? The article contains a link to a News item in UbiBlog
dated April 19, 2017,http://blog.ubi.com/ubisoft-expanding-europe-new-studios-opening-bordeaux-berlin/
which says the following:
"The team in Berlin will work closely with the BlueByte teams in both Düsseldorf and Mainz on an unannounced AAA project, and will help Ubisoft establish a presence in the German capital."
I saw no direct mentions of the platform or genre of the unannounced project there, other than: "Germany is home to Blue Byte, one of the most established names in German gaming and an industry leader in PC strategy games.", which can only be considered an indirect indication of the game's strategic genre and PC platform.
I checked what information was available on the Blue Byte website itself in my favorite section—vacancies...
Here, for example, is information from a game engine programmer vacancy:
https://www.bluebyte.com/en/career/vacancies#sr-post-id=743999660914438
"The newly established Ubisoft Berlin studio is set to continue contributing to this impressive line-up and will be working on AAA Co-Development projects together with international Ubisoft teams. The first project will be a big AAA-brand, one of the biggest and most important for Ubisoft."

Undoubtedly, the Might & Magic franchise fits the definition of one of the largest and perhaps most important for Ubisoft, but this is clearly not enough to draw conclusions.
There is also an application form on the Blue Byte website for those wishing to register as testers; in it, unfortunately, in the game preferences section, I saw no division between RTS and TBS, let alone any mention of Heroes. Along with other genres, it simply says: "Strategy (Star Craft, Civilization, XCOM…)", otherwise that would have been a huge spoiler. :)
It is quite possible that ANNO 1800 was hidden behind the unannounced project—which Blue Byte is currently working on and which was announced in August 2017 at Gamescom—but on the other hand, on October 18, 2017, already after the announcement of ANNO 1800, a post appeared on Facebook regarding a vacancy for a Community Strategist:
https://www.facebook.com/UbisoftBlueByteEN/photos/a.1040251262700174.1073741828.995469347178366/1623897734335521/?type=1&theater
The description of this vacancy on the site says the following: "Working with an exciting brand on an unannounced project, the position will be responsible for the strategic management of communities with a global focus."

Meaning that a certain unannounced project belonging to some exciting brand figures again, and they are looking for someone to work with the community... sounds painfully familiar, doesn't it? :D Could this project be Heroes 8? - It is impossible to say for sure yet, but there is potential.
P.S. How serious could all this be? - Time will tell.
For now, we can go back a bit into the past and compare it with the case when everything turned out to be serious:
http://www.might-and-magic.ru/blog/1/entry-3-might-and-magic-heroes-7-razrabatyvaetsya-v-limbic/