Can you solo ultimate quests eventually?

With fully upgraded gear and such, can you solo ultimate quests? Or is it always group oriented?

When Scion/Successor classes come out, yes.

imo by the time you can solo Ultimate Quests better content will be available

What solo content can I do (that isn't an event or temporary) that drops 13 star gear?

EDIT: Also, is the loot that drops in ultimate quest exclusive to ultimate quests or can all that 13 star gear drop in all stages that drop 13 star gear?

You can always solo it, even with +10 Nox. Units might be a greater problem if you want to do it without dying though. Either way the quest has no fail condition as you can always come back to the campship and try again. If you just want to clear it regardless of rank you want to rush to the last area. If you want to clear it with A or S rank you need to kill a good amount of mobs before going to the final area and not die too many times, with one death disqualifying (but only if you come back to campship instead of using a half doll or a moon atomizer in a party) you from S rank. So if we're talking about clear only really A or S rank is challenging somewhat but can be done with any gear depending how hard you want it to be.

If you're just talking about being able to kill mobs and bosses efficiently solo, then I think a fully upgraded Nemesis + Brissa set should be more than enough, but you also kinda need to know what to do and have efficient class combo. It's never efficient from drops perspective though as more MPA members increase spawns amount even if they themselves by chance don't contribute much to the damage.

pretty soloable right now with a good launcher+cosmo breaking and a nice rifle for bossing, but the boss spawns won't be as good solo in an MPA regardless of how strong you are.

Can you solo them? Yes, even now but not effectively. By the time you can solo them effectively they will be irrelevant.

It's doable right now, and I'm a fighter who spends most of the time in 25% hp (around 300-400hp) because of overload using only knuckles. It's just not effective to farm it while you are alone because

  • Having more people in a party increases your drop rate
  • It's just not fast enough

The real question might be: "If I'm not good at the game right now, will it be possible to solo ultimate quest if I get overgeared/overleveled?"