There's no evidence that this is the case, especially with the knowledge that the rate of expansion is increasing over time: https://en.wikipedia.org/wiki/Accelerating_expansion_of_the_...

And this has been going on for ages and we simply are universe X in time.

Alternative hypothesis the OP seems to refer to is the one of Lee Smolin in which a black hole from a previous universe creates a new universe. Smolin wrote a book about his theory, The Life of the Cosmos. I haven't read it nor do I know / understand his theory fully, so interested to learn others viewpoint on this theory.

Yes, that was my case (2). Spatiotemporal marble bounded by big bang and expansion edge. But it's not very satisfying - what is outside? Why?

It does align w/ the "eternal recurrence" concept.