The mod is currently back in active development (more precisely, being reworked). Given the upcoming amount of changes, the next version will not be 0.4, but most likely directly 1.0.

First of all, the changes will affect the launcher: fixing problems with the patcher and adding new functions to it; improvements to scanning (it will become much faster, and adding new mods/changing old ones will no longer require a full scan). It will be possible to enable/disable any of the installed mods.
The interface for disabling creatures/heroes will be improved and supplemented with all the necessary information about each hero/creature (taking into account the installed mods).
Similarly, the ability to enable/disable the generation of individual artifacts will be added.
For now, there are no plans for a lot of new game content; the focus is mainly on fixing problems with the current version.
NAF will continue to be developed; the plan is to add new sets for the remaining factions (currently, there are new sets only for dwarves and mages).
There will probably be new upgradeable artifacts.
Several new NHF heroes will be added, mainly with specializations based on the new features added to the patcher.

It is quite difficult to name a specific release date; about 60% of the above is ready, so I will risk saying the first half of July.