A couple days ago a site claimed a DMC4 demo ONLY for the XBLM is planned for a December release. Here is the article.
However, a confirmed Capcom representative on a Capcom forum had this to say on the matter (the matter being "Why the fuck is it not coming to the PSN?"):
This is clearly implying a near simultaneous release of DMC4 demo for both PSN/XBLA in December before the end of the year. The official DMC4 site will update on the 5th of December with news of this so keep that site on check for next week.
Originally Posted by Capcom Rep
"Wait a little while longer and the demo strategy will be clear.
I'll say this: The information printed above and in that article as written is incorrect.
The news you're looking for is not far off... a little more patience please."
Here is a picture of the Mission that will be in the Demo:
(It's from the PS3 version by the way)
Some notes about the demo:
*90% chance the demo will be the exact same as the demo we have seen since January. A quick walkthrough of Fortuna with Tutorial for a span of 10 minutes. After you beat that area you get to go straight to the icy level and fight a group of Frosts. The final mission in the demo will be the fight with Berial. This type of pacing/level design is not at all a representative of the final game as the demo seems to be snippets of 3 missions worked into one package as a bare bones demonstration of Nero's capabilities.
*These mini-missions are selectable from the start and you can choose whatever you want. Observe the first image to better understand what I mean to say.
*Do not expect Dante playable and do not expect the new jungle areas with Blades and Echidna or the new Lucifer/Gilgamesh weapon. I am not saying for a fact that they will not be in the demo, I am just saying that chances are likely they will not be.
*No story driven cutscenes will be shown in the demo aside from maybe the first cutscene of the game. Capcom is keeping the story underwraps very heavily. You will have cutscenes but they will mostly precede enemy encounters and do not at all reflect the main storyline of the game.
*Nero will not have any abilities outside of Snatch, Buster, Exceed, his gun and sword combos.
Be sure you know what is expected so you guys don't come in with the bitch fest of what is or what isn't in the demo. I am just stating this for the record in advance. Now peace out and discuss about the upcoming demo! :D