Welcome to the club.
The last time I saw a compatibility issue comparable to the RF3-to-RF4 conversion is was when Microsoft swapped out Visual Basic for VB.Net. I am very displeased, since
Java is known for providing backwards compatibility and migration paths and RichFaces 4 provides neither. Your news on RF 5 make it look even less attractive.
At a rough guess, expect IE8 compatibility to start evaporating in February 2016. That's about when Microsoft says that they're going to cut the cord. Anyone who's working for a company that's doing new development using RichFaces 3 that cannot migrate by then should be sending out their CVs now. I certainly am.
PrimeFaces or IceFaces are probably your best bets, although there's still stuff like the Apache MyFaces and Oracle JSF stuff whose name I forget, but whose functionality is supposedly replicated in MyFaces Trinidad(?)
I wouldn't seriously consider raw jQuery, since you'd have to move out of JSF and its benefits and besides many of the JSF extensions - including RichFaces - use jQuery under the hood anyway. Might as well get the jQuery with the automated MVC/validation/error reporting/navigation.
AngularJs and similar trendy things have their adherents, but Angular has now been around long enough for its warts to become apparent.