I don't think it's asset loading as such...it's probably has more to do with you leaving normal SC than everyone can connect to no matter if they have the expansion or not and then entering a mode of travel that only Horizons owners can connect to. That hand off must happen somewhere during descent after all.
The planets are already done in the same way as the examples you listed even if we so far haven't had the terrain displacement enabled/implemented.
The planets are already done in the same way as the examples you listed even if we so far haven't had the terrain displacement enabled/implemented.