To add... I honestly already feel we pretty much have this feature just in a different set up? Set aside the currently online status under the character and sorting from newest to oldest... Since you can search by multiple tags (it kinda sounds redundant and if anything 'restrictive' since we do have more freedom with custom fields/tags.) but.. it is up to the users to properly tag -- but only if they wish to do so etc. Which is less structured than having set fields, but I think that works well for a site that is flexible kinda leaves it up to the user to use it how they see fit whether its for keeping story ideas/ adopting/ rping/ etc...
Agreed with a masterthread idea.. making a thread (potentially request for sticked?) in worlds for RPers in worlds about potentially getting together in properly tagging your RP characters as "Seeking RP" or "Roleplay" to be easier...+ since there are custom fields, apart from the ones the site offers things like feral/furry/human can be added into the mix along with those you've listed from the site. I do think enough RPers go into worlds forum for it to catch on?
But.. an RP forum distinct from the worlds forum would be very nice for those who are looking for worlds to join vs those who want an rp.
I do think RPguild would probs be the pick if your focus was specifically RP though.