Well, for those of you wanting the enemy to remain a secret until launch might be disappointed. In the bulletin it states that they are preparing screenshots, weapons, characters, and ENEMIES to show off at e3. This could be just new classes of Covenant, not the main enemy, but it is a possibility.
I think its more likely they will reveal the knew faction, I mean how many covenant species can you introduce that weren’t in the previous games
probably the two from the toy package 
Well, these forums may be censored but not the world gaming sites or magazines, since the “elephant is out of the closet” we might as well look at it, instead of pretending it’s not there and we know nothing about it. However, I doubt 343i will spoil anything important, they’ll just give us a few pics and some general info I assume
I don’t think their going to give any thought to making new Covenant for this game since the Covenant will only be a side enemy, included only for the purpose of some classic gameplay.
Well, I meant the new, well, designs of Covenant
Keep in mind that there are more enemies than just the ones that were leaked, so probably a few will be seen, but not all.
They will probably show most of the the enemies, some of the classes, and have a little glimpse to the leader of the enemies in the end, like the concept art trailer, the thing in the end of it.