I find it hard to believe the supermarket category would be uncapped given that even the Rewards+ is capped at 6k and that is only paying 2x.
If it is uncapped, not going to last long, but then again Citi changes the cards around constantly anyway.
For existing users, it's a good deal through April 2021 since you retain all the old benefits, get none of the drawbacks, and get the new benefits. It's after April 2021 that things change and the value proposition becomes weaker.