There won't be a new Arc this year, that's now how Sonos releases their product. If they release a new Arc (gen2) it will be later this year or a year from now. Having said that, I am not sure what they would change besides maybe the internal hardware? Maybe USB-C?
Sonos targets two new products per year so they already did it with Era.
Beam is perfect for 32” TVs. Arc is perfect for 55” TVs.
1) I can see a super sized soundbar for bigger TVs. Mainstream public who exclusively use soundbars are also buying bigger and bigger TVs.
2) Sonos Amp cannot use the Era 300 as rears. Just Arc and Beam. It’s probably the CPU. So I would be willing to bet that you need a faster CPU to handle 4 Era300+Era Soundbar as center channel. That would probably be a very enjoyable HT on par with premium systems constrained by the same dimensions.