This isn't really a framework issue as much as an overall corporate process issue. The bigger the organization, the more documentation and details it tends to require (which is antithetic to the agile process, but I digress...)
I am thinking of defining different components of this framework by establishing patterns in areas such as interaction design,accessibility,information capture etc.
That is an excellent idea, and a common one. A 'pattern library' is an indispensable tool for UX teams. I personally feel that it is the one UX produced bit of documentation that has the greatest ROI.
But keep in mind that won't cover the breadth of the acceptance criteria. A pattern library is really for dealing with consistent interaction and visual design—both extremely important—but not necessarily the only bits of acceptance criteria you will find.
My purely personal opinion and not backed up with research (so take it all with a huge grain of salt) is that acceptance criteria should be written in-sync with Agile process.
In other words, creating the acceptance criteria is not a particular step in the Agile process, but merely something that happens as the Agile process unfolds.
- User story is written
- UX begins sketching
- As UX works with the stakeholders (IT, business, Project Management, etc.) Acceptance criteria begin to get fleshed out.
- As the sketching process continues, ACs are revised as well.
- Development picks up the features to be implemented in the next sprint.
- During the spring, ACs are revised further as needed.
- At the end of the sprint, consensus has to be reached that the developed product meets the ACs and—this is the key to me—that the ACs meet the developed product.
In other words, the ACs are part of the sketching process until the very end. They don't dictate the solution, nor are they beholden to it. They are a partner and work along side with the solution as it's fleshed out. They aren't set in stone until the Agile process winds its way to the end where there's something to deliver at the end of a sprint. At that point, the ACs are 'solidified' and typically handed off to the QA team.