in the future, I see no need to reinvent the wheel. WoW's dungeon finder is near flawless...
Its definitely nowhere near flawless. It solved a few problems and introduced a whole raft of much worse ones - At the heart of it, the dungeon finder is completely indiscriminate and it removed players' options to control who gets to join their group.
When they replaced the LFG tool with the Dungeon finder, they removed the ability for people to have a say in who they were grouped with when using the tool, and at the same time removed the mechanism which allowed people to avoid all the well-known idiots or give preference to people who they had previously enjoyed playing with instead (Who would you rather play with? Someone who was fun to play with before? or someone who you met in a previous run who was rude and abusive?).
The fact that cross-server communication is impossible in WoW is another flaw with the cross-server part of it (although that could be solved in theory by having ways in which communities can form across multiple servers). There's nothing at all in WoW which lets players have the opportunity to filter out idiots from other servers, or even to know who those idiots are
The only way a Dungeon Finder can work is if there are ways in which players can keep control and override the automation (The old WoW LFG tool had an "auto accept invite" checkbox, but most people actually preferred not to use it). A minority of people are always going to act like chumps; the community needs a way to make those people known, and players need a way to avoid them; When something like that exists, then people who are rude, obnoxious and foul-mouthed will all either find themselves excluded from groups, or they'll learn the hard way how to be polite and respectful to other players - 5 years of the old WoW LFG tool before the dungeon finder shows that community self regulation can work very well