Let's imagine Halo 4's CTF settings in a 16 player environment. Player grabs flag sitting in the middle of nowhere on Halo 4's wonderful BTB maps, entire enemy team's reticules magnetize to the fat waypoint over his head, player dies in a heartbeat. Fun stuff.
Extraction is super boring from what I've seen of it in Crimson. A very passive gametype.
Point is, unless they come up with some gametype settings that are way better than what we have, might as well just keep it slayer only. Do it right or don't do it at all.
Extraction would be vastly improved if there was only a single point to "extract" on the map at a time. As it stands now I had most of my games end after 5-7 minutes and my kill death was average around 4 kills and 3 deaths. There's simply no reason to attack the other base (and it often proves impossible to attack it anyway - by the time you kill one or two of the defenders, die, respawn, and start back to that base it's already been extracted).
Extraction with a single base to capture would work similar to King of the Hill; although the twist would be that you need to take over, activate, control, and hold until extraction to score any points. After the base is "extracted" it moves to another location providing a reason for teams to continue to move around the map (all while keeping a focused "kill box" or "action point" centered on the current base).
With two points on the map, and the size of the maps, you spend 85% of each map simply sprinting from point to point, pressing a button, and then waiting around for the off chance that an enemy decides to lone wolf it against your well entrenched (and rightfully
camping defending) full team. The current setup boils down to whichever team can sprint to the next base the quickest and bonus points are awarded for actually avoiding the other team (you get to that button faster = you win).