"Square also said on the call that the company doesn’t plan on offering users other cryptocurrencies outside of bitcoin. The company said it is focused on building its hardware wallet and continuing plans to allow individuals and businesses to mine bitcoin. CEO Jack Dorsey initially alluded to the latter plan in a tweet several weeks ago."
My mistake, margin low on Cash App. And it wasn't majority, in Q3 SQ's Bitcoin revenue was about 47% of net revenue (1.8b out of 3.8b). Bitcoin related only about 4% of GP at this stage.
Still, a very hefty slice of the business and I'd imagine the scaling of Cash App is a big part of the value.
Judging by the quote above, SQ wants to go even further in BTC. Its essentially worthless, but let's see long the party lasts, maybe years.