The Eleven Rack Editor is surprisingly easy to use with touch. You won't even need to use your Surface Pen. This would be a great setup for a gig or practice just to have access to the Eleven Rack Editor and the ability to Load and Save Rigs.
Pro Tools is another story for touch. Pro Tools is not built for touch, that is obvious, but it is usable. Adding in a Type Cover and Surface Pro Pen will be a must. The Eleven Rack works just fine with Pro Tools on our Surface Pro 3. Recording and playback works. Of course the issue would be the Surface has one USB port. We need a minimum of two USB ports for the iLok and Eleven Rack - so you will need a USB hub or the Surface Pro Dock to use Pro Tools and the Eleven Rack at the same time.
If I were going to do serious recording I would add in an external USB hard drive (or two), and attach a USB wireless full size Keyboard and Mouse. And if a full size monitor were available, I would utilize the Mini DisplayPort out on the Surface Pro 3 as well.
It's pretty cool that you can use the Eleven Rack and Pro Tools on a tablet. Once these things get more powerful, like quad core, dual SSDs, better video chips, 16+GB ram, they will be the way to go for every application. Just think about being able to have your desktop computer and all the programs you have installed on it - available to you at all times, in any location, and it's only the size of a tablet! That's the solution I am waiting for.
But, as it stands now.... The Surface Pro 3 (and 4) are pretty good at running Pro Tools. We are constrained by things like, one hard drive, one USB port, which means for serious editing you will need to add several accessories (USB HDD, Type Cover, USB Hub/Dock, Pen) which makes it less of a mobile solution vs. a nice laptop.
BUT! It's really cool to literally have Pro Tools and the Eleven Rack controls in the palm of your hand.