The possibility of going full frame in future was in the front of my mind when I bought my new scope, so I bought the version with the 3" focuser. If the little bit of vignetting I saw in the corners with my wifes DSLR was from the end of the drawtube not the 2" filter (Vic at Stellarvue warned that a little vignetting was likely with a 2" filter in the image train) I reckon I could live with it and as you say, flats would mostly deal with it anyway.
This is an uncropped stack of 21 X 30 second subs with my wifes D3. It has not done anything to convince me full frame with my scope is a bad idea. I did not quite have the spacing right but the clouds were coming so I took what I could get.
Full res on Astrobin
https://www.astrobin.com/full/lus2xa/0/