And another idea worded unneedingly restrictive: why doing that only for LDAP? It's the old feature of "username and displayed name" (old because there were boards long times ago where one could do that, unbound to LDAP).
smileypk wrote:Somewhere in phpBB, there will need to be an option that reads something like "Show user's full name instead of username
That is what you want, and you should have stopped right there. But your words mean that there'd be the feature of a displayed name that would otherwise be unusable to every owner not using LDAP.
However, keep in mind that this is also asking for trouble as then most (if not all) users cannot distinguish between username and displayed name anymore - if you ask for one of both they'll surely answer with the wrong one. Not to think about how addressing PMs and searching members will ever work...