I haven't noticed any rate limiters and there's no rate limit headers set so you could (not that you should) just brute force that. Names can't be 1 letter, they can't have 3 same letters in a row, they can't have numbers, case insensitive, maximum length is like 12, 16 at most, don't have the client handy.
Even if there's no limiters in place, you should limit it to something reasonable, 20 per second is well bellow "I'm a dick" bar. Other than that there's no other way to get player names. As with all things, don't abuse anything and I don't think anyone would mind. Cloudflare might flag you as a crawler/spammer so this may not work, I haven't tried it, don't need it.
As a side note, it would be great if we could only obtain some data. Like if you're checking class ratios, levels, races and factions, you don't need all of the data about gear and professions. Filters would be very nice to have.