This is trivially and virtually costlessly done in an automated way,
taking about a day of  a good programmer's time.   Thereafter
zero/minimal maintenance except for 'exception' followups.

One  informs registrants that  CONTINUOUSLY working
contact modes (e-mail, fax, phone, postal, say at least three of four)
are mandatory to avoid suspension/rescission.

Then one automates a routine to transmit tokenized letters/faxes/
calls/e-mails on a periodic but random basis, with the covering
message stating that the token must be returned on a website
within x days according to the terms of registration.   If sufficient
tokens to not appear, suspension  occurs automatically, just as if
you don't pay your credit card bill or pay your phone bill.

This is easy stuff.