Guess I'll be the first, what would be huge, and not complex would be to have class set up Main action bar templates:
Warriors - Stances
Druid - Forms
Rogue - Stealth etc.
While doable now, your normal Tom, Dick, nor Harry wouldn't understand the way we have it set up now, to do it by linking a bar with buttons to an empty bar that is bound to a stance yada yada, don't have to explain it to you, its your addon!!!
Since macaroon is my favorite addon, its the only addon forum I have subscribed to send me emails, and even I get tired of seeing hundreds of the same thread of "how do I set up my forms on my druid", so I can imagine you poor guys when you have to answer it over and over.
So that I think would be huge and a win win for you guys, cuts down the tech support needed, lowers the general learning curb, plus you guys on your end set it up once, of course with the flexibility that is loved, and all are happy. Plus making those templates 6 paged just like the blizz bars.
2. Also with dual spec, have some sort of option, to copy the exact layout to the 2ndary spec.
Example:
Lets say a non-hybrid class a rogue, now when setting up my bars, it takes time, to strategically setup my complex macros for one spec, but with a rogue you may only have 3-4 abilities different between specs that need to be changed. So with this option, when you elect to have that bar work as a 2ndary spec, you just change those 3-4 buttons and be done, instead of re-inputting every single macro for every single button.
Think about it on a normal main bar that's 12x6 pages minimum, multiplied by however many alts you have
.
Edit: You finish all 7 alts and the next day, OMG Maul all my buttons erased, lol, j/k as far as the stability of that, I don't know what you could do.