I don't think 4 needs an update or would benefit from this engine. A lot of the appeal of the remakes is the splicing of old school Resi with the RE4 viewpoint. A remake of 4 would likely miss 50% of the point.
As for Resi 1, Lost In Nightmares gives the closest approximation of what a re-remake of that would play like - and is probably the only vaguely positively thing to come out of RE5.
Meanwhile, CV and Zero are terrible experiences so I'm not sure where the remakes go from here. That said I would probably still buy a CV remake even though that game is just miserable from start to finish.
Enjoying 3make so far!