I suspect it will turn out like "WT under SoD" — neither side will like it.
Even TE-Light didn't catch on, although there were practically no differences from SoD gameplay. To be fair, that was in the pre-HD era; now it's easier with interface add-ons.
As for "writing your own Heroes engine" — there is a project called VCMI where people are doing exactly that. You can study their experience.