It's completely possible they only release to the next generation of PlayStation.
After all we will be at early access for about a year, and the devs confirmed that consoles will come alongside the full-release, PS5 will probably be on the market already. If the game stays in early access for about a year the full-release will be on 2021 and PS5 will be already on the market or at least has high chances that will be.
So yes, we can talk about future consoles for Mount&Blade II Bannerlord.
Even if it releases on PS4, it will surely release for its next generation (PS5).