The filter overdrive topography is possibly reversed, so you cannot do direct A/B comparisons
I have both, I definitely prefer the driven nature of the filter/drive revision on mk2, but I also like the Mk1 - so it’s one of those keep both scenarios, the A4 is a SwissKnife anyway, so utilitarian and reliable
The Mk1 will probably get every easy mod (if any incoming) - but there will be many it won’t (if any) - especially workflow synergies with DIGIs - there’s no need for them to sink time developing and testing such niceties on Mk1 imho, but there would be benefit in them keeping the save file structure compatible, so the feature set will evolve (which it probably won’t) - so really I think the Mk1 is quite feature complete - but if there’s a bit of added sound flexibility introduced I’d expect them to aim to support both still.
This can’t go on forever, but whilst it can and it makes sense I think it’s reasonable to expect some synergy
WRT the sound difference, it’s supposedly worthwhile trying to compare the bipolar drive behaviours in opposite directions on the two devices - so you cannot compare like for like potentially when using a midi cable between both. It’s identical in the Oscillator front, with perhaps a nicer presentation through the slightly tweaked output stage brought in for the AK. Otherwise no difference, and it’s a subjective thing, in some ways the A4 Mk1 may present a sound more to your liking despite the added Mk2 polish. Tonnes of threads on the differences. The OSs are still refreshed together, so there’s no sign yet that has changed, but it will probably happen - especially on OB bandwidth related issues as the Mk1s cannot be optimised in line with the improvements available with the flexibility offered with the higher bandwidth on the Mk2s