In regards to the idea of a "wow dungeon finder system", I have a couple of of arguments against it. First, an issue I have with the current wow dungeon finder system in the game is the time discrepancy between dps, healer, and tank. If you're a rogue and sign up for the dungeon finder, you can expect 17 minute wait times. Tanks click the button and get in. Healers wait 2-3 minutes. Would this same thing happen, with top and mid being in the dps, jungle being in tank (new players don't like jungling) and support/adc being the healer?
With my first argument being more of practicality argument, my second is more of an ideological one. By reinforcing the need for there to be a top laner, mid laner, jungler, adc, and support, it does kind of hurt any meta change that may occur, and also pigeonholes certain champions to certain roles. The day may come where we have adc solo lanes, double brusier bot lanes, or mid/support lanes. Who knows, the meta shifts and that's the fun thing. However, if we implement the need for certain roles, we definitely slow down, if not altogether stop this shift. Plus this is more of a hunch, but once you lay out certain roles, I feel like players will even more strongly associate certain champions to these roles, and even more experimentation will be stifled.
Alas, this is just my two cents, hopefully it'll help ya Lyte