Someone back there asked about the physics of the bubble shield. It rolls downhill in the alpha, but it won't in the beta. As for protection, it wont guard you against vehicles or people, only explosions and projectiles.
X button function, in case you don't know already, is the 'deploy' button. Certain objects, one of each kind on a map, will be deployable. Announced ones include the bubble shield and the trip mine, the portable grav lift has been shown, but theories also suggest a so called EMP mine, but I thin thats unnecessary with the trip mine.
Early in the ViDoc, I saw someone walking around with some sort of pole. sounds like the object engine they had discussed in a quick release a while ago. They have made the engine, but are unsure on whether to include it in the final game.
As for the pistol or magnum thing, I think they'll have both, as they brought back the assault rifle, and kept the battle rifle. MAybe they'll do the same for the pistol.
It shows the holstered weapons on your back or thigh holsters depending on the weapon. Strangely, the energy sword, which now has a battery life, is carried on the thigh. I think this may open up oppurtunities to hold dual wieded weapons on both thighs, though the way they talked about the dual wielded weapon problem makes this unlikely in my opinion.
I think the 'chaingun' is just a new weapon. Though, knowing bungie, its probably Frankie twisting his words. Not denying it but saying enough to dissuade rumours.
The so called 'new coagulation' mentioned before is Valhalla I believe. Its in the Beta as well as Snowbound and High Ground.
There. Hope I helped out.