Are +1 through +4 boss encounters placeholders?

Had that thought earlier today. In PoE through all the years it had been mostly established that multiple iterations of the same content are lame. That's why 3 consecutive campaign playthroughs eventually became one long campaign.

For the campaign in PoE2 this logic is also applied to the campaign: Going through acts 1-3 again is officially a bandaid until acts 4-6 are done.

So I wonder, will Arbiter etc be an exception where we don't get better than Greater Rift +1 or might we get a new boss for every tier like in Sanctum?

We had fire. There could be cold, lightning, shadow and more.