Halo 2 on Xbox 360 won't start

That isn't going to happen. At all. Games take years to produce. A 360 version of Halo 5 has not even been started, so even if they did start making it (which they won't), you won't see it for a number of years.

Let me put it this way for you. Back in 2007 Halo 3 was released on the 360, but not on the original Xbox. The reason they did that is to sell Xbox 360 consoles. History is just repeating itself.

They won't. The whole point of the collection is for it to be only on X1, they won't remaster Halo 2 for the collection and then for 360. Too much time and money spent.

The new xbox won't come out at least for a other 2-3 years, would be so stupid to release halo 4 on 360 just to have a new xbox comming out months after halo 4 and gta5 being released.

With the new CE Anniversary I would start there. It is the start of the Halo trilogy. There is the Halo Wars game, which is a RTS style game (think Command and Conquer) and it takes place before CE, though most won't consider it part of the MC line. And
Halo 2 is an Xbox original title, but it is backwards compatable with the 360. Just the mp nolonger works. Then the Halo 3 is the final game of the MC trilogy. You can find it used at GameStop or Ebay for $5. Halo Reach is also a good one and is sort-of tied
to the MC trilogy. It takes place before Halo CE and where it ends is where CEA begins. Hope this helps.

I know Halo 2 is on the computer and still playable(You even appear online on Xbox Live when you play it). You can get a adapter to use your 360 controller on the PC.

But, as other said they won't come up with a remastered Halo 2 until the 10 year anniversary.