No surprise, there. Given how successful Stellaris has been for Paradox -- despite its various issues -- I wouldn't have imagined they were done with the DLC train anytime soon. I expect Stellaris will see at least a couple more major expansions, along with whatever additional story packs and race packs get released between now and the end of the game's development.
There's also the variable of other Paradox games in the pipeline: We know about Vicky 3, I have to believe EU5 is in the works as well (for a whole host of reasons), and it won't be too much longer before it's time to start planning for HoI 5 (if they haven't already). Plus, who knows whether they have "smaller" projects like another Sengoku or March of the Eagles in development? Combined with the fact that they have only so many people to work on major game projects at a time, that necessarily stretches things out.
Given all that, I would be astonished if a sequel to Stellaris were released before 2023 at the very earliest, with 2024 or even 2025 striking me as being much more likely. in the meantime, Paradox has every reason to continue to make DLC for the current game, considering its success to date.
All *that* being said, there's one (possibly interesting?) thing I noticed... Henrik Fåhraeus, who was both lead designer and game director for Stellaris until he left the project to (as it turned out) star work on Crusader Kings III, seems to have dropped off the radar since CK3 was announced last year. Wouldn't it be funny if he was already starting work on Stellaris 2?
I realize it's a tad unlikely, but it's amusing to think about.