[andrewflnr]

Actually, cell-level endosymbiosis seems to have happened a bunch of times. Chloroplasts in plants are basically the same deal. The amoeboid paulinella chromatophora seems to have an independent lineage of chloroplasts. The Wikipedia page on endosymbiosis has more examples. It's starting to look pretty common.

Also, complex multicellularity (IIRC defined as differentiated cells) has evolved (according to the latest theory) six times. So that looks pretty likely to happen eventually, as well.

Human-level technological civilization, yeah, that looks like a one-time thing so far.

Edit: check out this article: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3910982/ They just casually mention "diatom-derived plastids", which are basically organelles that used to be diatoms, eukaryotic organisms in themselves!