Blazing Blade is one of my favourite games so it would be cool for a remake as long as it was as high quality as SoV. Some stuff I can think of is
Make Lyn mode optional (for the first playthrough) or at least make the tutorial optional
Make Eliwood hard mode playable from the start but Hector mode (and HHM) has to be unlocked from beating Eliwood mode
Skills would be nice but arts could be used like in SoV I suppose
Get rid of the support limit, I'd say either make it like SoV were you can have as many supports as you want and the characters have canon pairings that they end up with or add in S supports which could either be platonic or romantic and limit those to one per character so there are still different endings
I forget where I heard this but maybe make Leila the playable thief in Lyn mode so we actually care about her later instead of just feeling bad for Matthew
Give Eliwood an earlier promotion in his mode and make Lyn better in general
Make bows better, or at least make the bow using units not suck
Memory prisms. Stuff like Lyn's village being destroyed, Hector and Eliwood's friendship when they were younger, the Black Fang when they were still "good", Athos and Nergal's past, Nils and Ninian's relationship with Nergal, etc
Maybe give Mark dialogue but don't make them playable, if they do then don't make him a fourth lord
Maybe some OCs? The ones in SoV (aside from Faye) were really good and if the same team worked on it again I could definitely see them being great characters
Ability to marry Florina and Lyn