The 50+ and 50++ content is doing the other faction's level 1-50 content
Level-50 dungeons would be a good thing. But rather than uber gear as the reward, it should be crates of supplies consisting of rare crafting components or raw materials that can be used by a lot of people. Now we are talking rare stuff that you might find one or two of out of a hundred in normal resource gathering efforts. These crates would have a very large number of these, which could be spread out over time to maximize their worth.
The objective of these solo-raids would be to find anything that might be of use to the faction.
Like I said, at endgame it needs to stop being about "just me" and start being about community contribution. Even if the means by which I contribute do not involve grouping with others. I may not have trade skills that use certain raw materials or components I may find in a solo dungeon. But I know that others will be able to use them. this will help drive the player-driven economy.
And in my opinion, in the battle at Cydodiil, there should be a lot of things that need constructing that can be destroyed and need replacing, hence am on-going demand for crafters both back home and in the field. Crafters don't necessarily have to keep making and selling armor and weapons to the same players to be effective. But every crafting profession needs to have end-game applications so when they reach that stage there is always a need for their services.
Siege engines and the components needed to keep them in working order. travel rations to aid the movement of troops and goods between keeps under factional control. Weapons and armor crafted and submitted to "the troops" to increase offensive and defensive bonuses for those regions kept well supplied.