Nothing forces you to apply for a trademark. You can just accept that people may use the term "blockclock" to talk about block clocks.

Coinkite is also a trademarked term, and it's a distinctive one that I have no issue with. They can just call their product a Coinkite Blockclock and everything would be fine.

Anyway, this is irrelevant here: the competition they're threatening used the term BTClock. Which ironically is arguably _more_ distinctive than Blockclock due to the distinct spelling.