I have seen many people hating on loadouts and others that want them and wonder why they are not in the beta. 343i has said over and over that this beta is the arena multiplayer beta, which leads me to believe that there would be other modes as well, including the Infinity Slayer with loadouts we had in Halo 4 (though modified).
The way I see it, the Arena mode will be for all the ranked playlists and have 4v4, 2v2, 1v1, 8v8, ctf, etc, all ranked. Then there would be an infinity slayer mode (also known as casual, or non-ranked) that includes everything else. Action sack, loadouts, ordinance drops, etc.
I do not see a negative to this, as those who like the competitive side can play their ranked Arena modes, as those who just want to play around could do anything in the other mode.