According to Mithion, it is so far only allowed in Drewolf20's pack plus one other. So basically, Direwolf20's, and just one of those that you mentioned.1.5 Ultimate and maybe Magic World should also have it.
Are there any plans on adding ars magica to the direwolf pack in the near future?
It is highly likely he will start a new season (and new world) for 1.5/1.6So far even FTB doesn't have permission to distribute Ars Magica. Only DW20. And he's said on at least 4 occasions I can think of offhand that he intends to fold it into his pack.
But his single player pack is in a really bad place. It effectively cannot be updated without destroying a lot of the automation from his single player world, as it stands. For example, his nuclear reactor, sorting system, and potion brewing system will all break if he were to update today. So it's not clear when he will actually do that.
He may have insider information on upcoming mod updates; or it may just be that he doesn't want to introduce this break in his SP series. I dunno.
It is highly likely he will start a new season (and new world) for 1.5/1.6
Well, nor does he have ridiculously expensive EE2 items anymore either. I think he will finish up this season when all the mods he wants are ready and stable, although that may not be for some time now. When he talks about Tinker's Contract and Ars Magica being put in a pack, he keeps saying 1.5/1.6. That suggests that he doesn't really think that he will be starting season 6 until 1.6 comes around.That'd be sad. He's barely gotten started with his current world. He's nowhere near where he was when he stopped season 4.