Actually that isn't what Apple has been talking about. There are folks who attempted to listen to what Apple was saying and they said Apple was trying to get native iOS apps onto macOS, but that isn't it.
What Apple has actually talked about publicly is actually closer to a system where developers could write an app that has iOS and macOS components in it and that larger app bundle could run on iOS or macOS. Developers would were closely following the rules and guidelines would still have to do unique for iPads and Macs. And later iPads , Macs , and iPhones. The UIs would be different enough so that if had any substantive parts you'd have to do some work.
There would probably be a fallback and run in funny shaped window mode. For example, same thing that happens when run Instagram on an iPad. It just starts up and looks like the phone app. Kind of embarrassing but allowed one the one hand, but definitely not going to get any praise at all from Apple.
Those apps can be compiled into x86 versions just fine. ( they are now for the few that Apple did themselves. I can't see how it would get harder over the next year or two). The whole point is that you wouldn't need an ARM chip to run those.
[ The other Apple hasn't said anyting even remotely close to that thing is that T-series chips will get more horsepower and run abritrary user loaded apps. Not even close to what Apple probably is heading toward. Heck they can't even get their own software to run smoothly let alone Bubba's fart noise app. ]
No it wouldn't if those were just multiple iPad Pro processors soldered onto a single card. It would be like having multiple iPads inside the box but the individual software app on any one pf those wouldn't run substantively faster than on an iPad Pro. ( also would have the overhead of dragging the display result bak across the PCI-e connection. )
That would primarily only be handy for software that had the ability to 'run" work jobs deployed to a computational grid. ( like ship these jobs off the the render farm in the machine room. or farm these QA or compiles off to this set of remove machines. ). The 'front end' GUI part of the app collection results and manages tthe computation but it is carved up and sent off to instances. With a several ARM SoCs on a card they'd have a "cluster inside the box". Probably cheaper than the big cluster down the hall you might have to share , but wouldn't have to share.
Compressor can do these remote jobs but problem run into with small SoC is the size of individual jobs can do.
That kind of workload tends to get bounded into certain sub areas.
A CPU trying to take workload arway from a DSP may not work so well if can upgrade the DSP in the first place. Same card with ARM could be swapped out for card with more DSP/FPGA/ASIC etc.
thanks for you replies man, you two should get together and start a company or write a book or something! Your efforts are too much for a small forum