Street Fighter 4 is often seen as a game that revived the 2D fighting games, a game that brought the genre back in a big way and caused other publishers to follow suit. It's hard to deny its iconic status, but despite much respect and praise, you won't see too many people trying to play it these days.
The netcode is one of the biggest reasons behind it. Sure, age is a factor, but anyone who wants to run some sets in SF4 will have a terrible experience unless playing with people close to them, which might be either a small or non-existent amount of people.
Now, over 15 years later, it seems like the effort to make SF4 more playable online are underway.
It all blew up when Senor Power shared a Google doc on Twitter with instructions on how to get it installed and start playing. A very convoluted and scuffed process that involved either installing 3rd party apps or doing a decent amount of port forwarding. However, according to few people who got it running, it actually works, even if it's not even remotely close to a final and polished state.