Something I thought of last night instead of a remaster as such I'd love a version (Let's call it the ultimate edition) that combines GTA IV/EFLC meaning all side missions, weapons, vehicles etc each game introduced co-exist with each other and all the missions are placed in chronological order.
Of course you'd probably need GTA V's switching mechanic for it to work though. It'd be ambitious as hell, but that sounds more tantalising to me than a straight forward remaster. Can only dream.
If that happens I think there should be an option and you shouldn't be forced to play the missions in chronological order. Its nice to do once but at the end TLAD and TBOGT are just DLC's and I think that they take away from the impact of GTA IV's story (which is complete and rather long) if you divide the time between them.
I would definitely like to see all the weapons, vehicles etc. from the DLC in GTA IV though. And if they added the clubs to IV it would be hilarious to see Niko dancing.