Here's what I think would be desired:
1 Show Field of View (FOV) rectangle for camera lens/scope.
2 Allow placing overlapping FOV rectangles
3 Realistic light pollution simulation
4 Good catalog support for nebula, clusters, asterisms, etc.; so Messier and NGC objects (with pictures imbedded)
5 Catalog search
6 Realistic sky/atmosphere
7 Time control
I use Astroplanner, which is more of a planning app than a planetarium.
Of the features listed above, I know it will do #1, #4, #5, and #7. In the "Field of View" tab for a selected object in your plan, it will only show one FOV rectangle for the imager/telescope combination selected, but you can also move the FOV to guesstimate where each subsequent FOV needs to be pointed, and obtain the RA/DEC for the center of the new FOV pretty easily. You could then add that RA/DEC point to your plan (by right-clicking in the FOV and selecting "Add object to plan").
Astroplanner also does mount control, so you could easily construct a plan that contains one "object" for each panel of your mosaic, and then use AP to slew to each "object". I use an Astrotrac, so I don't do that, but it would be a useful feature for anyone with a more capable mount.
As for "Realistic light pollution simulation", I'm not sure exactly what you're looking for there - perhaps an estimate of the longest exposure you can do given sky brightness? If so, the developer (Paul Rodman) might be able to develop a script for that, assuming one doesn't already exist. And as for "realistic sky/atmosphere", AP can tell you the air mass and other extinction parameters for a given object at a given time, and you can also setup horizons for your observing locations, and AP will take those into account when calculating "visibility" for a given site and date/time.
It's powerful software, and I use it regularly at home and in the field. Probably the best fifty bucks I've ever spent in this hobby. It's not the only such software out there, but it's the one I use.
HTH,
Chris
