As a 4v4 player that generally plays successful runs with a higher number of consecutive wins (not to boast), I have come up with a few suggestions that may help enchance the gameplay.
1) Quicker round start times AND quicker round end times.
Reasoning behind is that, most of my matches last less than a minute, unless it's Crag or Priest matches. The round start time and round end time just keeps people waiting. In other words, they're unnecessary. Most of the time all I say is a Hall of Heroes mock message at the start, and gg at the end of the match.
If the start time was meant to be for establishing tactics and strats, most experienced teams should establish them BEFORE entering the arena. If the end time is for shit talking, the players leave too fast for a few phrases of shit talking.
What am I getting to here? Quicker times means quicker rounds, and quicker rounds means quicker faction, and quicker faction means quicker fun. Generally speed up the gameplay a whole lot.
I also acknowledge that it may screw up the whole time cycle of team matching and whatnot, but I am sure you GW developers will manage IF you decide to listen to this suggestion.

2) When the opposing team in the Crag all leaves (before the timer ends), end the match.
I don't see why this shouldn't be implemented.

3) Take out the Crag, or put it in a new selection of maps for a new kind of "most kill" game mode.
I think I speak for most 4v4ers when I say that The Crag is hated. I dislike it myself. It takes up too much time and detracts from the "quick" battles of Team Arena. So why not, have a new set of maps just for the "most kill" game mode. For example, since the Sorrow's Furnace update, I would really LOVE to play in a Sorrow's Furnace 4v4 arena with those gorgeous Crushers as environmental death traps.

Those are my suggestions, thankyou for your time,
Rusty.