@phinn
I don't know what major Linux distros mean, as I'm a decades long Slackware (& BSD) fan, kind of a Linux purist and adept of the KISS principle. nftabels was there since kernel 3.x (something) and iptables is still actively maintained. I don't believe there will be bugs the devs would need to care about, but implementation (understanding) and support issues. Furthermore, I believe it's mainly the LuCI devs benefiting from handling nftables instead of iptables.
Back to your point about some Linux distros adopting nftables as the main userspace tool for firewalling, just have a look at their support forums to learn how well it got received.
BTW, Ubuntu had its own struggle with it:
Well, I just expressed my opinion and advice. Until iptables is around and supported, I'll stick with it.