Good bloody question. Have to plead dirt ignorance about Rematrix or EW. Don't have either of them. Maybe nothing to be realized as far as an advantage with Reverberate as long as a stereo impulse can be loaded and some control over the mod, time stretch, normal ADSR envelopes. Independent loading of L/R IR routing which produces some desirable and unique effects. Very extensive eq control on Reverberate, about as good as Reaper's native eq.
Even Freeverb has a stereo engine for free. May work as well without the expense with a few less bells and whistles.
Just updated Reverberate since I had ver 1 and seemed like the right thing to do. Ver 2 definitely has some spatial improvements over whatever they explain about what's happening with their new stereo routing algos.
Excellent engine that will take a lot of time before it goes out of style.
Guess in my introspective journey as of late, if I had the same hard on creative insight I had when I was 16 years old... I would have died for a free reverb vst from 10 years ago and blown everything out of the water available today or tomorrow.
Not to be a downer, but suspect a lot of us like me are just accumulating debt and new plugs with nothing to show for it.
John