This is a rather interesting idea.
Personally, I think the GBA generation of games has the most
pleasant graphics, so to see a completed demake would be very
satisfying to me.
From what I understand there are certain inherent limitations
coding wise as to how many pokemon can fit the game, so
I believe, considering release order (and disregarding HG and SS since
they are remakes) that merging Unova and Sinnoh pokedexes would be nice.
Just my two cents anyhow.