I haven't read anything in this thread beyond the OP, but here goes.
Some overall comments. With a 2008 line-up that by any objective standards looks like it will be just as good as the PS3's, and only a single $50 price cut in the USA so far, not to mention a new chipset and the 360-mote hitting this year, the notion that the Xbox 360 has "little ammo left in it's guns" is absurd.
Last week the PS3 was riding high on a lift from the biggest Sony-associated franchise released thus far, and it still couldn't get 100k in front of the Xbox 360. Taking into account the holiday season, lets say the PS3 could outsell the Xbox 360 by 90k on average this year (and that is a VERY generous assumption for Sony):
6.3 million / 90k = 70.
SEVENTY weeks would have us in October 2009 before the PS3 overtook the Xbox 360, and thats assuming a 90k a week lead holds up in next years slow months. Putting that into the equation makes you realize the change-over is unlikely to happen until the middle of the holiday 2009. At least.
By this time, the next Xbox will be a year (two at most) away, and there would be no tangible benefit to any third party developer to go exclusive without moneyhatting (much like now).
This year in Japan, the Xbox 360 is getting just as many (perhaps more) big JRPG's than the PS3 is. And no MGS has sold more than a million copies in Japan.
Now that we have recognized the real-world situation, we can make some slight alterations to your questions before answering them to find something of relevance:
1. What can Sony do to ensure a change over by the end of 2009?
-First they need to ensure the quality of large, non-system-seller titles to sure up their stable like Resistance 2, Motorstorm 2 etc...
-Second, they need to make system selling titles available at a reasonable price (in other words get a price drop happening) and have the major system sellers that have been pushed back (GT5, FFXIII) arrive reasonably early next year.
-Third, they need to hope Microsoft keeps focusing on profit rather than sales.
2. What can Microsoft do to maintain it's lead long enough for Sony overtaking them to be profit/games library irrelevant?
-Having established profitability, use new chipsets to provide price cuts without sacrificing profitability. Be content to be profitable quarter-to-quarter, but not quite to make money on the Xbox 360 overall (in the next two years).
-Due to luck (Sony push-backs) and good management, Microsoft's sequels this year are just as strong as Sony's. However, the focus needs to be on games that can shift consoles such as Fable 2 and Banjo Kazooie 3, rather than big, non-system-seller titles like Gears of War 2 and Halo Wars.
-Right now, the new exclusive IP's the Xbox 360 is getting look just as good as the PS3's. Microsoft needs to ensure that they really are that good in reality.