Drual 7.61 was released a few days ago and I notice now "fully supports PHP 7.2". So, can we move to PHP 7.2 for CiviCRM where it runs with Drupal 7.61? I've updated a couple of my Civi sites to Drupal 7.6.1. and PHP 7.2 and all seems well, but when I look at stats.civicrm.org there seems very few sites running PHP 7.2 which makes me wonder why. So it is OK to move a Civi site to PHP 7.2?
The latest versions of CiviCRM run fine with PHP 7.2. However, a) this has only been true a few months, b) Drupal 7 has only very recently become 7.2-compatible, c) most major Linux distributions don't ship with 7.2 by default. I'd say those three factors account for few sites running it.
Note that as of CiviCRM 5.8.0, known PHP 7.2 import issues have been fixed. CiviCRM 5.9.0 will handle the other known PHP 7.2 issue, which only occurs on certain types of reports.