The new weekly episodes will be able to be done by all levels. I think down the road though, they should redistribute the missions so that they're more even across levels, using the new missions.
Why bother? It's not like the ships or personnel of the enemy factions actually change with your level. They might as well just make every mission level-scaling and just group them in chains. Then you'd at least have a choice of not doing everything in the exact same order with each alt...
Gamma Orionis has story missions. And it opens up at RA3 doesn't it?
And there's 4 new story arc missions for RAU+.
I've probably done them all already. At present, I'm grinding diplomatic missions to rank that up and I guess if I do enough of them, accompanied with the local exploration missions that go with the area, it makes it a little easier to rank, but it's taking forever. lol
I could always rerun Infected or the Cure, but those can take forever just to complete, so probably best the way I'm doing it now.