There might be some more modules like php-ldap or php-mcrypt but yes, we just need to make nextcloud use /opt/php-fpm instead of using rh-php72-php-fpm (which is just a TCP port configuration change) and it should work.
Maybe we could adapt nethserver-rh-php71-php-fpm in a way the /opt/ php version is used, then we could put the complete neth arm php 7 dependencies in one customized package and any neth php7 app should work, just an idea…