I agree, I think the celebrity boxing link will last a year or two, then it will fizzle.
However there's nothing stopping a boxing promoter taking, say, Triller's model of mixing both boxing and MMA fights to create interesting cards.
ONE Championship already does this at a high profile level with Muay Thai & Kickboxing as well as MMA, only there's no money in Muay Thai or Kickboxing; the future, for sure, is boxing & MMA events.
While it probably won't happen right away, it would be remarkably easy for Francis N'Gannou & Tyson Fury to co-promote:
Fury vs Usyk (Boxing)
N'Gannou vs Bhullar (MMA)
Etc.
The two winners meet in first boxing, then MMA, whatever you want.
(I only mention Bhullar as he's under the same representation of N'Gannou, so it's theoretically possible going forward).
These guys are going to get WAY bigger pay days than anything the UFC can offer, because the UFC has forged itself into this massive machine that doesn't actually pay the fighters well enough despite all the extra benefits.
I don't see this just going away now that the movers and shakers in MMA aren't just MMA agents wanting MMA fights for their MMA fighters.