krs,
Campaigns - one of biggest missing features for H3, requested a lot by players who are not interested in mods.
unicode support/i18n - needed for better support for localized versions of H3. Including mods. Right now it is impossible to (for example) install Russian mod into Polish version of H3.
launcher - needs some internal improvements, probably smallest feature from this list.
32-bit graphics - SDL 2.0 or not code majority of code that assumes that all images are 8-bit still needs rewrite/fixes, most notably - battles.
There would never be a single opinion on what feature should have highest priority - you want submods, some H3 players want campaigns, artists want 32 bit, on bugtracker there is request for unicode from Chinese players.
How many times I should repeat this: implementing even “special” field is far from trivial. Simplest example: random town was set to Castle or Rampart in editor. Now you made this factions “special”. How such situation should be resolved? This is most trivial example that I can think of even without looking in code.
If somebody will make bug-free patch that implement this then I’ll commit it. But othervice I’m not interested in working on this feature at this point.