Oddbean new post about login | logout This was mocked up on the phone but uses desktop modal, would need some tweaking for mobile replies, but similar concept. Pressing new account button would generate a new npub every time and automatically switch you (hopefully).
Switching btw different real keys is hard (impossible with browser extensions, possible with Nostr Connect or local nsecs), but switching to Anon is trivial, apps can just have a switch "Reply as anon" and sign this particular event with burner keys. zapthreads comment widget deployed on habla.news has that