Firstly I suggest you read Tom's reasons not to mix (which is about mixing AA with first arc but mostly would apply to XI too). If you want to create a custom deck then go for it, but it will probably work better if you are aware of the designer's reasons for not mixing all the cards.
Orb related powers and mechanic ( tooooo slow )
I'd just ignore the powers as you would with takeovers (though there are only two cards with orb powers + some* (4?) 6-cost devs which score for orb tokens.
* The fact I need to think about this despite playing AA over 100 times tell you I'm quite good at ignoring these...
Maybe someone had my idea with some playtesting.
There are threads in the AA variants forum - e.g. Four-expansion custom mix. I've thought about building a custom card list but I haven't for a couple of reasons:
1. I don't think I have played enough to make a decent list or tell whether a list I came up with was broken (base + AA being the only format I have played over 100 times, I've only played RvI ~30 times and don't own BoW)
2. It would take a while to come up with something and if I used the physical cards (which would be my preference) then we would be unable to play an official format whilst I was doing it.
3. I could just play RvI more, get BoW or XI.
I'll admit that it is something I like the idea of trying at some point, and I'll certainly read your list if you post it in the variants forum.