I think when wolves den first came out there were serious balance issues which led to the restriction of 1 ranged, 1 melee dps (ex: Summoners being able to cast raise), but I don't think this is an issue any longer. I think removing the 1 ranged / 1 melee restriction would be great, and it might also be fine lifting the 1 tank restriction.

There would be serious issues if you were allowed to have more than 1 healer, such as games lasting forever, but outside of this it would be great if you were allowed to change jobs within the staging area before the gates opened. There are incentives to have more well-rounded parties (VIT buff / support from tanks, strong burn from melee dps, CC from ranged) which would keep most groups balanced while allowing people to try out some interesting party compositions. The current system of diminishing CC resist would also help avoid job stacking.