I think in terms of fan service, Yoshi-P is mostly showing us the big guns in terms of concept art and screenshots. These are things like Dragoon, Titan, Crystals, Chocobos, etc. He's also shown us a revamped version of the Yellow Dragon from IV, as well as Demon Wall from various games (starting from IV). I'm sure once the game is actually in motion we'll start to see more of the original ideas.

I do remember hearing he's interested in concluding 1.0's original story.