Very timely question: I'm in the process right now because my current Model S has a sticker that expired in 2019, so I'm looking into trading in (or selling) my current S for another Tesla.

I don't know if the whole sticker option will disappear after 2023, but if it is still available then the "trade in" option will still be viable. It's expensive, though (not unlike a lease actually, since you end up selling/buying with a periodicity of about 3-4 years).