Rei only could after fusing with Adam's foetus and Lilith. The forbidden union. I would assume that if Kaworu called "eh good enough" on Lilith and fused with her (so again the forbidden union), then we would in fact see a GNK that can do all the same stuff as GNR.
Or, you know, if Kaworu and Rei bang
Well, I mean, I agree entirely. Poor guy is as lonely as you can possibly be, being Adamite in a world of Lilim and all. Just, you know, not from Rei
Asuka/Shinji: OURS! SHE IS ALL OURS! OUR PRECCCCIOUS!
Though, I did manage to think of a drawback of the Israfel Special:
Shinji can't become Shinji Soryu. After all, barring some rather unlikely changes in Japanese marriage law as a result of 2I, that would leave Rei out