The main problem with an iPad based Rails development workflow is that you can’t run code locally. You have to find a way to host and run your web apps on a server somewhere.
You can use an iPad Pro as a web developer, but you can’t use an iPad Pro for web development. The code has to run elsewhere, so you’ll have to use a second computer to do the actual development work.
I love the idea of an iPad being my only computer, but using a second computer behind the scenes when I need to do real work feels like cheating.