I don't like the idea.
Aside from the game going to become outdated again anyway (in 5-10 years), I bet Microsoft will ruin the one thing I actually enjoyed in Halo CE.
I'm an old Marathon player (the game bungie made before Halo), and I liked the references to Marathon in the series (the symbol, rampant AIs, mythical extinct race of aliens), that were removed or severely dumbed down in Halo 3 ODST and Halo: Reach. I don't want to play as another faceless soldier, there are plenty of games that do that. I do want to play a game that has a storyline that is so intricate, you can discover events that happened over 100,000+ years in the past, and still be shocked by it.*
*Mostly thinking of the Halo 3 terminals, between Diadict and Librarian.
Maybe the market has changed, and maybe the cynics are right, Halo's market are those who ignore the singleplayer and focus on "OMG! HEADSHOT LOLOLOL". If so, I'd be surprised if some of these aren't changed by Microsoft, who already removed mention of Marathon in Reach, and I bet wouldn't be above changing the singleplayer to suit the current market.