Don’t have a risc tablet but the consideration is the same as any other type of chip: what distro are you using and do the apps you want to use offer packages or source code for it? Before ARM took off this was the same problem. I was able to run an ARM version of Debian that had most packages I wanted and for others I could find precompiled ARM deb packages, but for a non-zero number I couldn’t find any and would have to compile from source code if available.
You’re gonna run into the same issue here, unless you find a lot of precompiled packages for what you want. Expect to do a lot of your own compiling.
Besides the other reasons here the biggest reason IM took off is the “I” part of the name. Email measures its SLAs in days. A lot of the retry intervals are set 4 hours with timeouts of 72 hours. It wasn’t designed to be “Instant”. Granted probably 90%+ of email gets delivered in under 5 minutes, but imagine having a chat and your responses are delayed 4 hours. Just send an email at that point.