UE4, tool bag, and the vieports for substance designer & substance painter all support realtime PBR right? If so, wouldn't the viewports from the Allegorithmic indie pack be sufficient? Iirc, they don't support post effects though...or is there some other reason it's not advisable for anyone to just use those?
I don't believe you are missing much, dunno why someone wouldn't just buy UE4 and cancel its like 19 bucks, has all the same PBR, and you get to learn and own a fully formed game engine..... seems a bit odd to me someone would go with marmoset now UE4 is live.