I like this! Could it be a plugin?
« Opening up » reaction types once a member has a certain mileage in the community would help keep things more bare-bones for people who are just arriving.
I personally love all the features that Discourse has for users and mods but getting it all in the interface upon arrival, particularly for non-technical users, can be a bit much.
(Drifting: there is a bit of this in how TL progression unlocks features but I think it could be taken a step further, particularly with the non-technical user on the lower end of the digital literacy continuum.)