I wouldn't know as a percentage. I will say that many of those present knew of blockchain technologies, as there have been several talks on it in the past, but it didn't seem to be a very big topic of conversation this year.

In the past they covered ways to come up with keys for (BTC) wallets that were created via the brain wallet method and how to steal coins that way, but even though there have been huge issues lately with wallets making use of unsecured local loopback-only services that several in-the-wild attacks have exploited via DNS rebinding, there was surprisingly little coverage of blockchain technologies beyond one talk that I saw regarding what block chains are good for.

Sadly, instead of learning about what recent or big new technologies or major security issues were coming (IoT Botnets, Spectre, Meltdown, subverting the IME, escaping sandboxes, etc) a lot of time was spent on politics, surveillance, and less technical content. If you google for how the conference went, you'll find lots of people complaining about MAGA hats, and how the conference was unfairly being fair to everyone instead of marginalizing anyone with a dissenting opinion. I'm sure that other stuff is important, but I'd much rather have spent time hearing about cool stuff that people were doing, like the guy that gave his entire presentation from a custom NES cartridge. Or the dude that made his own Amiibo emulator. Or the cool SPAKE crypto stuff that I only just heard about. But there were only a few of these technical talks.

Don't get me wrong, there was cool stuff going on, just not as much as there used to be.