Not so much an endgame improvement but a change to how long it takes to get to endgame.
I can think of various developments that could be developed from the suggestion of @mirroredhunter . Multiple fortresses (maybe 3 or 4 per sector) such that each layer of fortress needs to be killed before the next one can be hit, using the level rings as a the connection. This would mean that different alliances would need to work together or to move into every sector.
Each fortress linked by a hub group and the hubs blocked from attack until the previous level of fortress has completely been wiped out. The fortress could rebuild as it does now, but at a faster rate and much higher increase in level. The maximum level of a player to be increased to cope with the increase in the level of the fortress. The fortresses on the outer layer could be set at 45 in the 20 ring, 55 in the 30 ring and 65 at the 40 ring. The centre fortress could be set at 90 to start. Each time a fortress is killed then it increases by 15 with a maximum for each fortress of 255. Each fortress on a ring can increase beyond the level of the fortress on the next levels.
Make the world physically larger to cope if necessary, but don't increase the places proportionally. So a world with 30 000 spots could be 2x radius of existing 30 000 worlds. Ordinary forgotten bases could have a maximum of 75..... I'd also like to see the bases respawn with an increase of up to +5 of their previous level making it harder for the next alliance to follow through if they wait long enough for the forgotten to be respawning.
