Everyone’s SR would roughly double over time. The numbers of SR don’t actually matter. It’s a statistical distribution over all values.
They would need roughly twice as many rank “names”, and most people would be in the 4700 - 5200 area.
SR is not used for matchmaking, so there would be no impact.
No impact.
Right now, SR gains are limited as SR approaches 5000. It’s technically impossible to have an SR of 5000. If you got to 4999, wins would give you 0 SR. I think losses still give -24 at that high SR, so it makes it very difficult to get much higher than people do.