I think BOLT protocol is for Zcash and not bitcoin because it mentions in here:
Furthermore, Electronic Coin Company CEO Zooko Wilcox is advising Bolt Labs and helping the startup create its first proof-of-concept this summer for the privacy coin zcash, which doesn’t use lightning like bitcoin.
And here:
In order to be activated on the cryptocurrency, new code would need to be added to the zcash repository, in what is called a “soft fork” — or a type of change that doesn’t require all versions of the software to update.
Here is the links for the second quote:
In the end of the article, he conclude this:
And not only that, but going forward, Akinyele feels that BOLT could provide a private link between zcash, bitcoin and litecoin — a layer-two interoperability that he hopes could dismantle some of the tribalism that occurs in cryptocurrency today.
He concluded:
“It provides an option to figure out how we can get away from ‘this currency does this, this currency does that,’ and just start thinking more longer term and big picture with how we want to use these currencies in the real world.”
Which mean, there could be a private link between three coins or something like that.
But maybe I am wrong.
Besides of Zcash, I see it's related to XRP too.