I used to think that EU4 was a game still full of potential, which could still have a long shelf life to come, but last DD made me reassess that, I'm not so sure anymore.
That said, I don't think EU4's dev cycle ending will have so much to do with the game itself, but instead I believe EU5's development progress is what will dictate it.
If we are to take CK2/3 as reference (and it is the only one for current PDX business), EU4 should have its last expansion the year before EU5 is announced, which would mean EU5 won't be released for at least another two years, and probably more since Johan has implied that Leviathan won't be EU4's last DLC.
Then again, knowing that CK3 started development around 2015, I cannot imagine at all that EU5 isn't already in development, as that would imply a release after 2026, which to me seems rather absurd.
My guess is that we will have another two DLCs or so after Leviathan, throughout 2022, and in 2023 we'll get free patches similar to Great Works and Iron Century, with EU5 announcement towards the end of the year to be released in 2024.
Seeing lots of people saying no to EU5 because we don't have Vic3 yet. Those two are not related as far as I know, so working on one one should not impede the other.
You're probably right, but I imagine PDX wouldn't want to release or even announce both simultaneously, or within a short period.
They'd end up in direct competition with each other, which could affect sales.
So, while both games could very well be in development, the announcement of one most likely implies the other not coming for some time still.
Unless the pandemic threw PDX off their release schedule for last year, and now they have two games in the pipeline ready to come out, or something of the sort.