I believe the feedback is for once you get the Beta installed. At least, that's my understanding based on previous Betas I've been involved with.
No harm in sending them a msg now though.
You can get the Beta upgrade on any network. But your phone MUST be a BTU version, meaning you can use any SIM from any UK network in it and not just say an EE SIM for example.
Mines not a BTU it's a H3G (three network) but mine is factory unlocked, as three's policy is all Thier phones are unlocked, I am praying it means I can get the beta still :/
Yes it is meant to show up under Notices .
I've always had unlocked Galaxies (direct from Samsung shop) so can't comment on previous Beta releases but I have definitely read that for this, it needs to be a BTU phone.