If it had a really good selection of Snes N64 GC and DS games, as well as the online features wrapped into one £15ish a month payment...Well lets compare to other Netflix-like services we see on the Xbone and PS4. For Microsoft, the Xbox game pass is $10 a month. While for Sony, the PS Now service is $20 a month. (Keep in mind, the PS Now library is substantially larger than the Xbox game pass library, and it spans more previous Sony systems). At $20 a month including your online access fee a month getting a selection of ideally hundreds of games spanning the NES through the Gamecube, and the GB through DS. Its actually a price right in line with what the competition is doing. And of course if you paid a yearly fee you'd get a discount just as Sony and Microsoft's offering allow for.
Why wouldn't I want this? Having access to all the best old school games without having to pay for each of them individually would be a dream come true, especially for a system like the Switch that you can bring with you anywhere. I'd be all over it and I know I'm not even close to alone, I've floated this idea on other message boards (and other threads here in the past) and overall people seem excited by such an idea.
I'd pay for that yeah, there's a ton of games worth playing.
I wouldn't pay for just a bunch of gameboy nes and snes games though, I'd rather use my 3ds.