Well, I also didn’t exactly explain everything I need, just that I would need the global OSC control support
-> "global control" seems to be a buzzword for me. I think it makes more sense to describe the details step by step.
/ ability to access faders, solo buttons, etc without submix switching.
-> faders, solo, mute, global mute, global solo is currently possible for me? I am sure, you played around with the Routing Mode in TMFX in two windows at the same time (SUBMIX vs FREE) - each controlled by a different OSC Instance? maybe i didnt really understood what you mean...
What I mean with ”free control on multiple submixes”, is that I have to be able to keep multiple submixes partly in sync (some submixes with synced faders, some with synced faders + solo states etc.
-> i do not really understand what you mean. maybe its because it is already late night here 
more details?
And no, there’s not enough fader / solo groups on TMFX for this).
-> in my little world - 4 fader- (plus one adhoc), 4 mute- and 4 solo- groups are enough for each unit. but ok - you can adress this as a detailed feature request to rme, if you need more groups?
Also, I have to be able to keep the sync when controlling more than one fader at a time
-> exactly what i do - but i do it programatically in the OSC (software) controller(s). f. ex. i select by my own, which faders i select at the moment - and even independant of the submix settings of TMFX. of course: OSC is networrk based -> one command after another. but i have no latency issues (after lot of debugging). ok. not easy, but relizale to "self expand the fader groups".
, and not with latency added from a script that would only adjust the fader on a submix after I release the fader in another. I’m using multiple controllers too, so things would get really complicated / slow with scripting.
-> you talk about latency? but you use OSCulator? sorry - but its exactly the same i do in my "scripts". And i use multiple controllers, too. Which controllers exactly do you have? Connected via Wifi? If yes - please dont mention latency. On the other hand: both of us seem to have a complex/irregular environment. Its quite normal that there does not exist a allaround solution for everyone (in german: "Eierlegende Wollmilchsau", Joke). So, beeing creative is the best workaround for me.
On the other hand, with global OSC I could simply copy the OSC address of a fader to direct address (if the host is connected and acting as a kind of bridge) of a fader on another submix, for example with OSCulator, and I could choose which submixes receive values from which others, as TMFX would send out these direct values when adjusted.
Adding different controllers to this would be super simple too, no scripting necessary!
-> Sure - i also have a lot of ideas, espacially to implement idependant MIDI CC for each element in TMFX. Would be nice to control the units without a hos connection via USB. But i understand that it is surlely not easy - just because there are win/osx/iOS plattforms on the one side and all the Hardware Units on the other side which are parially introduced more than 10 years ago.
Moogs Model 15 App is a good example - although it is not possibble to map a certain MIDI Channel to a CC. But - its Okay. Have to do some workarounds...
I’ve pretty much maxed out what I can do with the current OSC implementation using multiple TMFX windows and OSC-addresses. There have been other users mentioning other scenarios where global OSC support would be needed. Automation of TMFX etc..
-> Maybe, its worth to dive in deeper. As i said before: OSC brings you the interface to get direct access. In complex environments, its worth to fiddle out the circumstances which match as good as possible for you. And what other people/users say is not really relevant (for me)
“Do It For Her”
My Gear: Bontempi Magic light Keyboard
And I understand that if your setup works for you, other people’s need are not that relevant. But that’s exactly why we need global OSC. It would really work for any situation and all the needs.