I'm not sure we ever talked about assigning multiple DRs to a single attribute but we did (and still do) talk about assigning both a DR and an AR to a single attribute. Part of this goal is to separate data access (DRs) and calculations (ARs) so calculation results can be exported to PI or other databases. In this line of thought, all the current 'calculation DRs' should be converted to ARs. We are currently in the process of refining the design for the next version of AF (2.2) so we'll have more details in the months to come.
So Formula DR will become Formula AR? Then an AFAttribute can have a PI Point DR as well as the AR to output the result of the Formula to a PI tag?
Will you be able to use an AR without scheduling it within a Model?
Appreciate design is not yet finalised, I just like to be prepared
(By the way, sign me up for any beta releases of AF 2.2)