"Slow money" in Neptune's Brood is a digital currency, and is confusingly referred to as a "bitcoin" a few times, but it's actually a really fascinating idea that's very different from BTC.

The gist of it, if I remember it right, is that all transactions are authenticated by an interstellar 2-phase commit handshake. The distances involved keep the value of the currency stable, because transactions can take decades to process, and the direction of the signal is actually used as a form of authentication, to guard against (literal) MITM attacks. The goal of slow money was to have a currency that was stable enough to finance multi-century interstellar colonization projects.

I suspect Stross may have been trolling, just to try to ward off the existential risk that bitcoin and autonomous economic entities edge us closer to. Either that or he's holding btc himself and figures that fomenting debate will be good for the value levitation.