Are there any plans to make a sixth installment in the Heroes series?

No one doubts that they will be released :) ;) We are more likely discussing what we would like them to be like))) although there are many such topics, but what can you do? :)
Nevertheless, I agree that it will take 1-2 years, although maybe even longer, the main thing is that a quality product is released.
As sad as it is to admit, the 4th part was released in a hurry. The game turned out to be good (it's actually my favorite part), but there are too many bugs in it, and that's very sad. Fewer hidden loopholes would be better.
You need to play using your mind, not the game's flaws, because this primarily harms the game itself....