Most games that only use boot block to load hardware loader should work fine unless they assume KS1.x like memory allocation and overwrite OS structures or do something stupid that only works on 1.x accidentally. (which is not rare, unfortunately)
100% compatibility is impossible. There is no way to make ROM that is both 1.3 and 3.0/3.1 compatible at the same time. Even 3.1 compatibility can't be 100% because it would require implementing all known and unknown bugs 100% exactly! (it is guaranteed there is at least one program that only works because of some OS bug..)
Examples of bugs we have seen:
- assuming that registers D2 to D4 can be modified in input handlers. (Only worked because AOS input.handler does not use those registers, of course they are not documented as being scratch registers)
- calling dos functions without dosbase in A6!
Both are worked around but not all can be fixed easily (or at all without breaking new aros-only features for example)
some update notes:
- real audio.device implemented but only minimal testing done (audio.device is rarely used for sound, usually only for channel allocation)
- first part of aros graphics modeid updates done, modeid and depth separated. Next part is to replace generated modeids with real AOS modeids.
btw, it is fully 68000 compatible (I have seen some strange notes somewhere else that says you need a 68020 or better)