I would much rather have the inquisitor have to learn to function with only one arm than anything else, my preferences would be as follows:
1) The inquisitor's arm stays as a useless stub and he has to learn to live with and fight with one arm.
2) An appliance is added but isn't mechanical. Something like Captain Hook
3) A mechanical arm that can fail or malfunction and cause drama
That is all.
Hell the 3rd option (or maybe even the second option) could make for some really interesting leveling up or weapon crafting mechanics. I'm not just making a weapon, I'm trying to make this crappy tech on my left side ... less crappy. Plus, to be fair all Inquisitors are right handed anyway. A prosthetic could be built to hold a bow, literally be a shield or dagger, have a focusing crystal, or for two handed users simply be a way to reinforce their grip allowing them to put some of the weapons weight back on their left shoulder. Maybe the thing never gets to function all that well, but some of the upgrades let you put extra consumables (like grenades) inside of it ... silly, but it would be fun and bringing back the Materials mechanic from Inquisition could let you at least customize it's durability or appearance.
I'm not expecting Automail here and I expect it to have serious problems and/or be painful (especially in the early game), but Dragon Age tech and magic should be perfectly capable of creating something usable and potentially give us a fun game mechanic to play around with.
Heck it might actually present an interesting dynamic verses Tevinter and Solas (both who put the past on a Pedestal) in of itself. Going after them using something as forward thinking as a prosthetic arm that could have only been conceived of or created in the current Thedas, where magic is heavily limited by the Veil and thus inter-racial interaction and cooperation is more the norm (Lets face it if there was no Veil, the Ancient Elves would have probably enslaved or ignored the other races). Fun stuff! 