I gave that a try, and I've tried several other combinations since. Nothing seems to avail.
For example, I have a very simple workflow that takes the selected text and wraps it in <sup></sup> (I do a lot of work with text that uses superscript). If I assign various shortcut key combinations (e.g., command+s, option+s, control+s or command+shift+s, option+shift+s & etc, or a symbol key or a number key) the workflow is not invoked.
I have also noticed some odd behavior in digging further into this.
If I assign a keyboard combination (say, command+i) to a workflow, pressing that key alone without the "modifier key" (in this example just the i key without the command key), I hear a clicking sound if that key is pressed immediately to the right of white space, either as the first character in a new paragraph or after a space between words.
However, if I press that key immediately after another character, with no intervening white space, the i character appears!
I've tried this with various keys, symbols and numbers and get the same behavior in each case.
So at the moment I'm stumped in re: the shortcut keys. I hope to find a solution soon, as this would be a very handy feature to have.
I am using a New Trent keyboard on my iPad Air, which is running the most up to date version of iOS 8.0.2