Call me crazy, but I don't see Goldeneye aging well.
It's a novelty at this point. Which is why I think it's a good thing they're not selling it individually.
I think they missed an opportunity not making the Xbox version online. Unless there is going to be some sort of update later. Really it would be ideal for an online game in this present gaming generation. Why go to the trouble of such an update and not include the multiplayer online?
There's a lot of speculation as to why. One of the more plausible reasons is that Nintendo's version gets online play automatically through their Online system. It's not actually programmed in the game. It's somewhat of a hack that Nintendo does for their other retro multiplayer games and this just came along for the ride.
Is there anything stopping Rare/Microsoft from programming in online? I don't think so. But it's also possible since it's a Nintendo 64 title, MS and Nintendo worked out some deal where both versions are different from each other. The Switch version is just an emulated version whereas the Xbox is actually remastered.