Milieu 0. You have a growing empire, huge frontier areas, massive options for political games, exploration games, colonization games, mercenary games, trading games, etc.
Everything I have heard people on here wanting from 1105 already exists in Milieu 0. So, a rewrite and rerelease of Milieu 0 would be amazing. Less TL12 through TL-15 and more TLs 5-12. Which is something I hear people on here say that they want. -30 to around the 120s would be a great setting for all types of campaigns. Droyne are unknown. Aslan are basically unknown. Hivers are unknown, K'kree are a rumor. Ancients in this time period are thought to be a branch of Humans. Psionics are not banned.
Etc...
Update Milieu 0 to MgT2 rules. Remove things that have been retconned. Smooth over stories that no longer fit with the MgT2 rules. Redesign all ships and other equipment to fit current rules. (or future rules in the case of the Vehicle Handbook)
Player Agency in Milieu 0 is far higher than in 1105. PCs can be a major part of the expansion or formation of the Third Imperium from the Sylean Federation, whereas in 1105 material, affecting the entire Imperium is basically impossible for a small group of PCs. In My games, We never deal with things that large in scope in 1105. In Milieu 0 rising or falling in social status is much easier than in 1105, which benefits the PCs more. Also, Meson Weapons, but no Meson Screens. Nuclear Dampers are brand new technology at TL-12. No sensors above Military Grade.
Etc...