@PerniciousPea even on PC (NA east for me), where the population is apparently not as good as it is on consoles, I have to focus on TT but GW sees matches that range from 6v6 to full, usually on the fuller side, GW2 may drop to 8v8 temporarily but it is often full (although hackers can be a pain, they aren't as rampant as some say), and BfN is harder to measure as people leave and bots pop in, but it was comparable to GW as far as population the last time I played.
So, if the least populated platform is still going well, and you can't get GW or GW2 on Steam which would likely make them perform even better where I play, then that means that XBox and Playstation are even more populated, plus the Switch for BfN only, a new game, if done well, would be at least as popular as the current stable of shooters as we're playing 3 games in maintenance mode, so people are slowly moving away as they feel 'done' with the games. If they can keep up a decent pace of new content on top of a great new game, something like the DLC we had for GW and GW2 early on, they could easily have another hit. We need new stuff to do in the established PvZ universe, as part of the fun is discovering stuff; this is why the backyard battleground from GW2 and the BfN free roam regions were so exciting. Stuff like finding the golden gnomes, solving puzzles, the snow globe hunt, and just finding new locations spark something within us.
This doesn't guarantee a new game, and many popular IPs have faded away (often from bad games or other issues), but it does indicate to EA/PopCap that there is a large audience for a new game. They just need to do it right.