That's 100% marketing talk. There will be no native running "full" Photoshop. Maybe it will be cloud hosted like on chromebooks but porting the behemoth that photoshop is is not gonna happen.
I don't doubt that Photoshop on a desktop machine will usually perform better. But the latest iPad Pro models have six-core 2.3GHz processors and 4GB of RAM. It was only a few years ago that were were doing pro photography work with machines of that specification.
The challenges are definitely going to be building a productive and useful UI using the iPad's input constraints. This is something that might be more effective on a device like the Surface. But I'm sure there are ways to build a good user experience on an iPad, so we'll need to wait and see what happens.
The iPad can almost certainly handle massive images just fine. The industry has been getting by with that sort of processing power for some time. I can't comment on support for 10k images specifically, but 4k video editing works pretty well, and 30MP+ images too (so 8k-ish?). And while there's a segment of pro work that needs 10k+ support, it's not everything – just because the whole professional market isn't supported doesn't mean a segment of it isn't! (I haven't had much call to edit anything in excess of 4k for a long while, despite using Photoshop pretty heavily).
The input methods might be a challenge, like I said, but it's possible to think of ways in which a good editing experience might be achieved, with the compromise being worth the trade-off in portability – but we'll need to wait and see before jumping to conclusions!
It's plainly obvious that not every professional user requires support for multi-gigabyte image files. I've never even used a workstation with 64GB of memory, despite being a professional Photoshop user for a long time.
Just a bit of a silly thing to complain about, really.
We're working on a 2D game. Some years ago, when PCs had lower amounts of RAM, games didn't even had to include full HD assets. These days you may even target 4K. While you're at such resolution already, you may even go a bit further and keep it at printable quality for easy marketing. This eats lots of resources, no iPad will be up to such task. It will work fine for occasional, amateur editing, with low resolutions and low amounts of layers, but definitely not in our professional case.