Is it a 5dr fastback / hatchback after all? It seems so:
5th door? A hatch? It seems very much so! Look at the inner cut line in the D-pillar.
[IMG]http://www.**************.com/community/attachments/hatch5-jpg.13555/[/IMG]
[IMG]http://www.**************.com/community/attachments/hatch-jpg.13551/[/IMG]
[IMG]http://www.**************.com/community/attachments/hatch2-jpg.13552/[/IMG]
[IMG]http://www.**************.com/community/attachments/hatch3-jpg.13553/[/IMG]
With clearly visible C-pillar (1) and rear seat belt housing positioned behind the pillar and below the 3rd side window (2):
[IMG]http://www.**************.com/community/attachments/hatch4-jpg.13554/[/IMG]
That means C-pillar is real, and the rear door opens to C-pillar only (like on GTs, Tourings & SAVs/SACs), not to D pillar (like on sedans or 6er Gran Coupe).
I'm trying to show the inner cut line in the D-pillar. Check it out how it looks eg. on 5er GT:
http://www.worldcarfans.com/11105233.../highphotos#18
Meaning the rear window opens together with the trunk lid ( = hatch door aka 5th door). And, yes there is a 3rd side window there, and therefore D-pillar as well.
Meaning 4er GC is actually a 4er GT after all: a hatchback/fastback 5dr coupe ala A5 Sportback.
Or perhaps BMW invested a lot in a fake interior camo (fake C-pillar, fake 3rd side window, fake seat belt housing under the fake 3rd side window, fake inner cladding of fake D-pillar - showing fake cut line) to make 4dr 4er GC looking like a 5dr coupe, a hatchback/fastback. But I see no point in such act. It's much more likely 4er GC is actually a 4er GT with 4 doors, not a GC with 4 doors like 6er GC.
PS: there will be frameless windows on 4er GC /GT - check the missing cut line in the B-pillar on the prototype in the spy pics. The blue render is wrong since it features it ... just like the "framefull" 3er Sedan in the spy photo. 3er GT comes with frameless windows as well.