I’d keep the TR-8 if you love the Scatter on it, you can for sure do interesting stuff with the scenes on Rytm but not in the same way as scatter, you could repitch, reverse, extend, shorten, filter, fx etc etc which of course can sound great, but it takes considerable effort to program then test/tweak, which is fine, but nowhere near the immediacy of scatter, albeit very flexible though.
A lot of people diss scatter, but I really like it, sure it can sound cheesy when overdone but by no means does it have to. I have a Scooper and the MX-1 and am very happy with them, keep debating to get a TR-8 but it is rather large and a bit fugly, but I think it sounds very nice, you might miss the sounds as the Rytm does not really cover the 808 sounds quite as effortlessly as the TR-8.