In theory, there can be multiple indexers, and you (or, at least, your PDS) would be able to choose between them. In practice, though, it's going to be incredibly costly to run an indexer, so expect corporations and VC-backed orgs to dominate. Bluesky has the first-to-market advantage, so they'll be the big one. Twitter could well pivot to indexing on the BS protocol. Maybe a few others will pop up. That's what decentralization really means here: Your choice of corporate-run indexers.
I'm sure there are people on the fediverse for whom that use-case is a good fit. They put a premium on account portability, can shoulder the technical burden, aren't concerned about the privacy implications, and aren't particularly invested in the more thorough-going decentralization. To them I say, good luck and God speed.
I just don't want anyone making that jump without recognizing that one choice they're being asked to make is between account portability and genuine decentralization.
/end
I'm sure there are people on the fediverse for whom that use-case is a good fit. They put a premium on account portability, can shoulder the technical burden, aren't concerned about the privacy implications, and aren't particularly invested in the more thorough-going decentralization. To them I say, good luck and God speed.