You'll still be left with 64ROPs (4SEs-16 each) but yeah point takenThe number of ROPs would seem to be one of the reasons for the improved game performance of Navi. Reducing ROP capabilities would also be detrimental to providing good performance as the target resolution for the next gen consoles will be 4k (by whatever means, but still).
7nm EUV seems more and more likely for nextgen so even with 128ROPs we are looking at ~370mm2 after factoring in design rules that prioritizes density over clock speed you mentioned