This is a solid concept...but potentially problematic. Anytime management brings in someone to "help" the Coach - there is a real potential for discomfort, especially if the Coach isn't asking for it. It's generally a shadow on his shoulder - your replacement on deck. It's needed, but most be handled very sensitively, imo. Also a slap in the face of the rest of the assistants, particularly any that are the alleged "offensive guys". I don't really give a crap about their feelings as a primary concern - in fact they NEED to be held accountable for the garbage offensive (lack of a) scheme they put out there all year...but, still, it's a sensitive thing and you want to handle it in the most positive way to get results.
On the good side, ORL never replaced the Lead Assistant that left (last summer?) So, it could be seen as filling that open slot more than getting Mose a better offensive guy to tell him what to do, because Mose has failed at it. I don't think Mose is insecure, but it's a dangerous dynamic regardless - to even seem to undermine your Head Coach.
Ladies & Gentlemen, I present Joe Ingles...he'd be low enough on the coaching totem pole that he wouldn't be considered "threatening" but he's just got the mind and the demeanor that the guys love and respond to. He'd be more like a vet leader, but he could really focus on working with guys like AB, Cole, TdS (whoever is still around) to slow down how they see how things unfold and speed up decisions. This vision is not the same as the OP, he probably wouldn't be elevated to the degree of re-writing the offensive game plan...he'd be more like the equivalent of a "Big Man Coach", like the guy that was brought in JUST to work with and babysit Dwight (Clifford Ray?)...he'd be the "BBIQ consultant"

I am not forgetting how often I say some things can't be taught, but if he could refine the way guys see things just 10% better...it's a big deal. He was a massive plus for our second unit in his brief stay here until he really wasn't able to play much in the second half of the season. If we bring in rookies with his kind of mature game (Wolf, Demin, etc), Ingles' mentorship could speed their development and integration that much faster.
Bringing in a big-name hired gun like Stotts or Mike D'Antoni would be tough to stomach and confusing. Mose is such a great player's coach - but it'd be undermining to bring in such a successful former Head Coach...the "hot seat" questions would be constant and, imo, unfair.
I thought I read recently that Ingles loves ORL and his family might even live here (or want to)