I think that many existing apps with huge userbases will gradually lose users as the models become better and better. Their biggest advantage is that people don't like change, and thus having to e.g. export data from some tools etc. seems to be a hassle not worth $5 a month. But as the models get better and the quality of the output will match the quality of the established SaaS but tailor the whole thing to a single user with the ability to make any change they can imagine within minutes, and perhaps deploy to Hetzner and whatnot where they could host all of those apps for a single $5 instead, the exodus will accelerate.
On the other hand, new products will have a much harder time to gather a big userbase. Whenever I'll see a launch of a SaaS asking for $$$, the first question I'll ask myself will be how long it will take LLM to recreate it. And for most cases, I imagine that the time it will take to get 80% of what they have is a few vibe coding sessions (as most newcomers will probably have used LLM themselves to code it up).