One compelling reason to upgrade is to get rid of that "completely freezes your computer when you quit the game from fullscreen, on a Mac" problem. It's an engine bug that they've fixed since the version AIW uses.
And in general there are a lot of improvements. I dunno if the GC situation itself gets any better. Though I think we may have substantially reduced the number of too-many-heap-sections crashes a few versions ago (albeit slightly increasing the number of out-of-memory ones while we did it, I still don't have enough data on that).
Anyway, my working-copy of the game (the one I actually modify directly when developing, and do all the first-line tests in) is actually on a more recent version of the engine, though not strictly the latest anymore. It works fine for the most part but the textboxes often get into a state where they are totally borked. I honestly don't see how to make the upgraded version eligible for public usage without simply writing a custom textbox class of our own. Before I did that I'd want to make sure AIW was using our latest GUI code (for which the _only_ remaining thing we use Unity's built-in gui for is the textbox)...
All told, a lot of work.
But the game can run on the later version, and it does work in native linux. But there's still critical things (mainly the textbox thing) that we've yet to work around before we could release it that way.
