Okay, quickly implemented the insert and hit the first very "big" issue.
In logging (but likely in other places as well), there is an insert like:
$id->insert('', '{db_prefix}log_online', array(...), array(..., 'IFNULL(INET_ATON(\'IP_ADDRESS\'))', '''));
So that, at the moment, it is translated to:
$doctrine->insert('elk_log_online', array(.... 'ip_something' => 'IFNULL(INET_ATON(\'IP_ADDRESS\'))', ...));
and of course it fails...
Well, that's all for today.