I think "have players online at any given time" is the tough part there, but it's also the tough part for many non-abstract games. If you look around on Board Game Arena you can see a number of abstract games available, but with many you'll struggle to find any other players.
There are some cool abstract games out there, but they're not super popular. Abalone was mentioned in another comment here. Octi is another cool one. Some like Azul or Patchwork have a light theme but it doesn't really affect the rules, mostly just an excuse for the piece design, which I think puts them in a similar category to chess.
I'm not sure I'd say we won't get another deeply studied game. I mean, if we're comparing to chess and go, it will take hundreds of years to really know if any modern game has that staying power, let alone remains interesting to analyze. But I do wonder if we'll ever get a game that's both deep and popular.
The popularity of RPGs, TCGs, and expansion-based games suggests to me that a lot of people really like feeling a sense of immersion into a "world" that's constantly revealing new "content", rather than discovering new variety within an existing system. Maybe this is just a stereotype, but I also feel like there's a synergy this and a similar vibe prominent in stuff like fanfic, where people like to engage in this sort of generative building on some core ideas. The "pure" or "cerebral" gamer who is really interested in the ramifications of a fixed ruleset is somewhat more rare. Also there are so many games out there now that even cerebral gamers may be tempted to explore new ones rather than digging deep into familiar ones.
This is just to say that maybe some existing abstract games are actually deep, but in order to know that, we'd need people to take the time to analyze them and explore them. Maybe time will tell.