I'm going to go out on a limb and say the next drop will be available March 20th for Elite premium, and the first DLC pack will be available to everyone else on xbox the end of April. Because of the Xbox/PS3 disparity and the Elite premium/non-premium disparity this season of content is not going to work out well.
If they release DLC every 4 weeks then Xbox Elite premium will get the last one Sept 4th. Then PS3 Elite premium will get it October 2 or 9, and that means Xbox non-premium shouldn't get it till Oct 10th at the earliest, and PS3 non-premium the first week of November when no one cares about MW3 and everyone has already put their pennies together for CoD9. That's called a clusterfuck.
How To Fix It?
First, get rid of the Xbox/PS3 disparity. There is already an assumed month between when Elite premium members get DLC and regular members get it. With the Xbox/PS3 thing it means that at minimum 2 months has to go by between the last Xbox premium release and the last PS3 regular release.
Second, work backwards from where you want the DLC releases to end. You don't want to cannibalize the next CoD title's marketing campaign by trying to hype DLC for the last game. To me it seems that the big push for a new CoD title release starts in August, and is in full swing by September. CoD XP was the beginning of September last year, and if they keep doing it that way everything about the current title will be completely drowned out by the upcoming title. That doesn't mean people don't still play the current game, but it does mean you won't be able to create any kind of buzz for DLC for it.
Activision/IW/Treyarch should aim to have the last DLC for the existing game completely released to everyone by the beginning of September right before the hype for the next game reaches it's zenith. Add in a month between Elite premium release and general public release and you end up with about 9 months between when the game comes out and when the last DLC should be released to Elite Premium members.
Let's add in 2.5 months at the very beginning of the game's cycle where there is no DLC to let everyone get used to the game (including a large contingent that buys the game at Christmas; this is a major part of sales that they can't ignore), and we have late January through early September, or 6.5 months of available DLC release time.
I think they made a mistake to promise monthly content, and to spread it out over 9 months. Here's what this year's season of content should have looked like without the Xbox PS3 disparity, and after what it should have looked like with the disparity:
Without Xbox/PS3 Disparity
January 24th - Elite Premium receive pieces 1-2 of DLC
February 21st - Elite Premium receive pieces 3-5 of DLC
March 20th - Elite Premium receive pieces 6-7 of DLC
April 17th - Elite Premium receive pieces 8-10 of DLC
May 15th - Elite Premium receive pieces 11-12 of DLC
June 12th - Elite Premium receive pieces 13-15 of DLC
July 10th - Elite Premium receive pieces 16-18 of DLC
August 7th - Elite Premium receive pieces 19-20 of DLC
March 20th - Regular members can buy pieces 1-5 of DLC as a package
May 15th - Regular members can buy pieces 6-10 of DLC as a package
July 10th - Regular members can buy pieces 11-15 of DLC as a package
September 4th - Regular members can buy pieces 16-20 of DLC as a package
With Xbox/PS3 Disparity
There's no way to do it right. Don't try.
And to tide over Elite premium members until the first pieces of DLC come out give out something like a prestige token with the game in early November, then again the first of December, then again the first of January (or at Christmas like they actually did 2 months ago). Something that's not officially part of the promised premium content, but that only premium members get.