The lack of mouse for text selection is a huge problem, and constantly switching between Safari and your code editor (I used Vim in a remote terminal) is a pain as well.
I actually didn't choose Vim because I liked it, but because it was the only way to have an editor & fully working Linux environment in the same app where I can switch using a keyboard shortcut (both running in Screen).
Using an app means that I have to switch apps to go between editor and terminal, and also because the editor app would have to "upload" every single change to the server for me to actually be able to run the new code in the terminal.
Anyway, I'm not trying to convince you an iPad is a sane, comfortable way to do the kind of programming where you are regularly doing a backend-to-browser sort of cycle. You can probably make it slightly less barebones 'terminal session to a server running vim'.
Not saying it’s sensible or a particularly nice experience, but it’s doable.
Pythonista is an app so powerful it’s surprising it was allowed into the store.
Also, couldn't you use vim shortcuts for text selection? I guess that wouldn't work in safari...