It's actually possible IMO.
The devs who create dll for AFM are generally not the same as the devs who create, tune and bench graphic engine for instance, and those are not the graphists who model the artwork of the aircraft.
So, parallel development is theoretically possible, isn't it?
For example, you personally are occupied with the design/texture/... of the mig-21bis art (among other aircraft I 'd guess) but AFM dll is for an other person, isn't it?
But I'm OK with you that some improvement are to be done in the code of DCS itself. EDGE is to come, dynamic campaign is a far dream and the 'gameplay', or what happen during missions is up to the missions designers.
Normal, is sulerly coding as hell thinking "I've said Sept 1st; what have I done, OMG, OMG, NO rest for the team until we have something to share for Sept 1st!!!"