If people are looking for the sort of startups that use .io can Google search on
site:.io
and go through first number of pages.
@James Iles did an analysis of the domain names used by about 1000 startups not long ago.
That study found that 7% were using .io vs about 60% using .com. The .io figure was almost double that for .net and .org
combined.
I don't think a highish renewal fee is a negative to an end user, and in fact the lower level of abuse with TLDs with high registration/renewal is a plus that is probably more important. The renewal fee does mean that domain investors must be selective in their .io holdings.
The interest in .io was in early years definitely within the coding community, propelled by some significant users. But now it is much broader, although not as broad as .co.
It remains to be seen whether the political efforts to repopulate the area will impact the view of .io. A few end users have left because of that controversy. That said, there is no sign of a weaker aftermarket, and the highest-ever reported sales in extension are in 2021, I believe.
As with anything, many things to consider.
Bob