Series 0 is slow enough as it is, I think it would be virtually unusable if apple slowed it down further. Unlike someone asking if Apple is doing this with the iPad (reasonable question and very possible), I don't think its likely for the series 0
Doubt it. WatchOS 4 has not performed all that well on the first Generation Watch to begin with. It's also under powered unless you're primarily using it for stock applications and tasks.