IRC population has also become harder to track because more people now set up cottage networks that have one server and only host a few channels. There was an article a few years ago discussing this exodus from big networks which I'm having trouble bringing up now.
The worst that can happen to IRC is something like Usenet's death - growing too popular to scale. But scaling isn't of primary importance because a network hosting 100,000 channels is only mildly more convenient than 100 networks hosting 1,000 channels each. Nobody wants a chat stream that looks like a popular Twitch channel, because there is no longer any signal when that happens, so big channels are outliers. (And Twitch chat is IRC-based itself - demonstrating how much this technology is a commodity.)
IRC isn't going to stagnate completely until people decide to give up on text-based chat. The main thing it has trouble with is new client features like inline images.
The worst that can happen to IRC is something like Usenet's death - growing too popular to scale. But scaling isn't of primary importance because a network hosting 100,000 channels is only mildly more convenient than 100 networks hosting 1,000 channels each. Nobody wants a chat stream that looks like a popular Twitch channel, because there is no longer any signal when that happens, so big channels are outliers. (And Twitch chat is IRC-based itself - demonstrating how much this technology is a commodity.)
IRC isn't going to stagnate completely until people decide to give up on text-based chat. The main thing it has trouble with is new client features like inline images.