I think te best way to milk the last couple years of McGregor would be to arrange a tournament to announce the 165 division, with the winner being awarded the belt. Do it similar to the WBSS where the top four seeds pick who they fight, that way if you stick McGregor on the 'easy' side of the draw, you're pretty much guaranteed three McGregor PPV's. Quarter final, semi final and the final.
Then after the tournament if he wins (or Nate won) he can defend/fight for the title Vs Nate III or if neither wins just do Nate III. Maybe do the Khabib rematch for the 165 title should McGregor still hold it after all this.
The GSP fight is definitely more sellable at 165 as well, it'd still be massive at 155 but who's to say GSP can even make 155 healthily.
I love the thought of the tournament, who would you have in it?
McGregor, GSP, Nate Diaz, Poirier, RDA, Cowboy Cerrone, Kevin Lee and maybe Michael Chiesa or Eddie Alvarez.
Keep Ferguson and Khabib out of it because that fight needs to happen for the 155 belt, regardless of how many times they've tried.