Chances are pretty much null that there will be a public beta given PDX track records so far.
It's not like their previous releaes of main titles were in a bad shape anyway (DLC is another story). CK3 had a very smooth release overall with very few bugs. The same goes for Imperator, the game did everything the way it was designed while being pretty much bug-free and with good performances overall. The main issues at release were that the game was centered around abstract mana and conquest, two things that the community grew tired of after 6+ years of Eu4. I honestly believe that Imperator would have been very well received had it came out 3 years earlier.
Regarding early access, The only major studio doing it in the strategy genre that comes to mind is Amplitude and even then they do so by working incrementally by adding more and more innovative features as development goes. I seriously doubt the same would work for any grand strategy made by Paradox Interactive since the mechanics are generally very intertwined to the point that none of them can work well in isolation if at all. It also wouldn't help the player experience that AI, performances, and balance, which are key aspects of PDX games, tend to be the last ones to be done.