Yes, guilds are supreme, but you could do a Trial Finder, but not in the same way Group Finder works. Instead, it could work more like the "Friends" page, which tells you who is online, where they are, etc.

For each character, you click an option that allows the game to input your role, class, stats, etc. onto a page that would be available to other players to see when you are online. You check boxes for what trials you are interested in doing on that character. And maybe even a line for notes to describe the role further You toggle the Trial Finder to be off if you want to be online but do not want to do a trial, and of course, have settings as to who can see your page, character, etc. So a page would look like:

Damage Dealer. Magicka Dragonknight, CP 1600. VHRC, VAA, VSS, VCR. Notes: 100K DPS, Can do Zens DK

On the other end, if someone was looking to put a raid together, they could go to the "Trial Finder" page, see who is available, click the box next to the players/roles they want, and that would send out invites to those players. It would tell the player who is sending the invite. Probably would need to put a cap on invites at one time to avoid spamming, but whatever. Its more of a known quantity than queueing in Group Finder

Obviously, there is room for people to embellish their DPS or lie about their accomplishments and people can be snobby about CP, but whatever. At its core, you know that you are inviting a DD Mag DK that is CP 1600 and what trials they will do, instead of watching Group Finder pop and find out you are going to Lair of Maarselok