While i love MGS4 and the MGS saga, it would be better for Kojima to develop a new game to give him a break from the series, and come back to MGS5 with fresh ideas later on.
From the pictures i've seen, Lord of Shadows looks very interesting and if its being partly or fully developed (im unsure) by Kojima Productions/Konami, then it should become a classic in its own right, given the magic touch by Kojima himself, even if it fails, I'm sure the Japanese fans and various worldwide fans will stay loyal and buy it.
There seems to be too many sequels and prequels in gaming, not enough new and fresh ideas.
Kojima likes to take a breather after MGS an usually releases a new game either form another of his franchises or a brand new one so, I do expect Lords of Shadow to be helmed by Kojima.
On the other hand production times and costs have risen and now a game takes almost 3 years to produce and costs as much. I expect that a new MGS by Kojima Productions not directed by Kojima will be announced shortly and it might be a remake of his previous MGS games using the assets created for MGS4.
Or it could also be a bunch of DLC to expand upon the main MGS4 game after the many expansions of MGO. Maybe even a 360 version if they manage to revamp the whole game and cram it into 5 DVDs and remove all the Sony and Apple references (gotta give 360 fans some hope, after all we got Bioshock and might get Tales of Vesperia in America).