I thought season 4 would be the end, especially as they teased the virus that kills sups.
Not sure how far they can stretch this.
I only really see it going two ways
A. EVERYONE gets powers, then after a bit of lunatic chaos, they settle on "if everyone has powers, then NO ONE has powers" and life goes back to normal.
B. NO ONE has powers (or all the supes get killed off) and after a bit of lunatic chaos, life goes back to normal.
Unless they go full on Injustice/Invincible/Irredeemable with Homelander attacking world governments and trying to run the whole show himself, there is really no where else to go. Maybe a "Butch/Homelander work together to stop (+/- working for Voight) supers infiltrating the US government" plotline but I dunno. The showrunners don't seem to really care about developing the corporate/political stuff beyond the bare minimum, it's just "new villain of the season" type stuff.