Xbox One

Partially right.

You are correct in the sense that it has a different architecture. In fact Xbox One went all out and got a "custom" x64 for unbeknownst reasons, couple this in with the fact that the Wii U runs on an x86 and so does the PS4 and you possibly no longer have the neat portability you had the last generation. Was bound to happen I suppose. Sony isn't making it work by "porting" anything what have you. They're using a streaming service that streams the video and takes in your input to a cloud service that plays the game for you. It is their whacked version of the virtual console.

However, this is where you're wrong. Nintendo has indeed done backwards compatibility by emulating them and that is very true. However the reason why emulating post-N64/PS1 consoles on the computer is hard is by no means due to the fact that it's difficult to emulate for the company making the consoles themselves, but rather because it is difficult to reverse engineer them completely. Take into consideration the fact that the companies themselves know all the ins and the outs of the system themselves, this makes the reverse engineering stage with disassembling, OAM, et al all considerably easy on their part. This is why it's hard to emulate -- because it's become harder to reverse engineer them.

Wii U is not x86, it's a modified Power PC.