For my part I dont want to buy it on EGS, because I prefer having everything under one roof. I can't do this for every case, but try to do so. Also, atleast for teh beginning - later than that I dont know - the EGS was supposed to be not safe and lacking functions. Until now I never was interested in any of their exclusive games, so I never read more into it.
(for the time when its coming hopefully on Steam), I'm most excited about the Data fights, where I managed to not spoiling myself on any of these (exceptions being the music and the Secret Boss).
As for mods... I guess modders could try to put the Data versions into the graveyard sequence, but since I dont know what the Data fights are made of (except being difficult), I don't know if these upgraded fights would be possible both technical wise and gameplaywise.