What similar things do people use now?
Those fields are actually built a bit deeply into SMF for some reason, so it's not completely trivial to change, but it can be done. Low on my to-do list, though, as hugeblack mentioned.
Ive long thought there should be a spot for PGP fingerprint.
PGP fingerprints are SHA-1, which is insecure. The OpenPGP standard really needs a complete new revision...
The point is that what they use today may change in 6 months. Most people use Telegram, discord, Twitter for issues related to crypto.
But I think it would be more interesting to leave an open box. Where we could organize the contacts in the way that was most interesting. Allowing to put the address of Bitcoin and other coins.