I think it will come out on the older gen machines. If GZ used the same engine, then it was at least capable of running on the older consoles at acceptable framerates. As to environments being larger, I think that only increases VRAM consumption, which the older consoles have anyway. Likely, it won't be playable at higher resultions than around 1080p or 720p but other than that, it should have very little difference in graphical demand than GZ. As for HDD space, most console games have encoded audio because the un-ues extra APU cores can decode it, so it won't be much of a space-hog either, especially on the current gen PS4 and Xbone.
I think the onlt thing that affects whether GZ comes out on last gen consoles is that if whether or not Konami is willing to port it from current gen to past gen, since GZ is obviously coded with current gen in mind. However, performance wise, it would be easier to port GZ to PC since current gen is closer to the power of PCs than past gen consoles. So, IMO it depends on whether they want to port it to PC or to past gen consoles or if they're lazy and don't want to do wither.