I don't think it's a V6. ETK already has the I6s for 6-cylinder representatives. The Scintilla doesn't really make sense with a smaller engine option alongside the 5.0 V10 when we see the reality of such cars. Unless of course we're talking about a smaller Civetta model, with an equally smaller engine (let's say a Twin-Turbo V6 or a Twin-Turbo V8).
I understand that they physically wouldn't be too large, but a twin turbo V8 would be more expensive to produce and engineer (the chassis only had inline engines before) and would likely have more power than they were looking for in an 800-Series (roughly 500 HP looking at Mercedes' 4.0TTV8) and significantly more than anyone would expect out of a BMW Z4/Mercedes SLK equivalent, which had a maximum of 335 hp and 416 hp respectively. 420-450 would likely be the upper limit of the 800 and K-Series cars which could easily be achieved by a modified I6 for less money and less time.
Still, the Hot-V design makes a V-engine more compact instead of traditionally having the headers and turbos sticking out on both sides, so it can also fit between the same frame rails of the engine bay without much, if any, modification needed. As for modding the I6, yep, the FCV approach, with multiple ECUs and turbos for each engine, should also apply to the modern ETK engines!
If the new update doesn't come out, I'll drink a glass of beer with black mold and no head. (Jk, ofc, please don't do that. Take your time. )
Have we abandoned the idea of a GT3/GT4 style K-Series? They might have made a widebody V8 version for homologation (honestly idk how those rules work but let me dream)