When I bought the Rytm I thought master FX would come in handy, but I never ended up using them. I just don't find them all that useful for percussive sounds. As for the samples, I don't see them lacking at all considering how open ended the synth engine is. They'll mostly be mangled beyond recognition or used for attack transients. Another thing is, I certainly wouldn't use the Curtis filter for lush or clean tones, but it has a dirtiness that's great for certain uses. I played an Ensoniq Esq-1 the other day and it sounded amazing. It may be crude by today's standards, albeit has character that's lacking tremendously in modern day equivalents. The Tempest is in the same territory, so the lack of reverb is not that crucial, unlike the OB-6 and P6 that are greatly hurt by not having a decent reverb like the super plate. The (possible) Tempest X may be amazing, but I don't see it having the character that the original has. I actually like the synth sounds that come out of it more than anything I've heard come out of the PX. Again, no sample hassle is also a huge plus for me. Ratchets (as Sequential is calling them), more robust external MIDI capabilities, & parameter locks will be a huge plus, but not worth what will be lost imo.
On a side note, the Rytm's filters while much more robust as far as modes are concerned, sounded weak-sauce no matter what imo. I couldn't find much reason to use them beyond the pads that could utilize the VCO engine. The cymbal engines were not to my taste and there's no reason to use the filters on the samples, beyond using them in conjunction with the noise generator that's available on those pads. And good lord, for that price, Elektron should have known better than to cut corners on something as massively important as decent pads.