I've had support for this since 2020-05-10, with the ability to store silo usernames to support @-mentioning on silos:
GET https://www-api.jvt.me/micropub?q=contact
{"contacts":[...,{"name":"Aaron Parecki","nickname":"aaronparecki.com","url":"https://aaronparecki.com/","silos":{"twitter":"aaronpk"},"_internal_url":"https://www.jvt.me/contacts/aaronparecki.com/"}]
by 
Jamie Tanna
.