Just a bunch of sparse and loosely related or unrelated thoughts:
1) By the time MS would possibly start using it, it wouldn't be decisive anymore for BD success as a format, so MS shouldn't have any problem about helping a format it didn't particularly like.
2) MS preferred HD-DVD and disliked BD also because the vast majority of HD-DVD players used MS licensed firmware for interactive contents, so making it earn license fees, while BD uses a Java derivative, and MS hates Java, but this shouldn't be a problem for games, as they don't use the very limited processing power present in players for interactive contents, games are heavyweight and largely more interactive programs that run on the main CPU, so they won't push Java popularity unless MS decide to program them in that language, not very likely.
3) As many of you wrote, Sony, despite being one of the biggest BDA members, is one of the many big ones, so it gets a small % share of royalties, and, if it's correct that Sony gets more on discs and Panasonic on drives, MS could always support BD playing compatibility, to offer a more complete multimedia machine, but go the Nintendo way using proprietary formatting for game discs, this way it should pay full royalties only on the drives, but it could just license from the single owners a small bunch of patents for the discs.
4) Curious thing: while obviously Sony gets the full profits from its own games and it gets also exclusive royalties on 3rd party games, like any other console architecture and brand owner, for what regards the BD royalties it earns only from 3rd party games, while on 1st party ones it just saves on them compared to game devs not member of BDA. The reason is simple maths: on 1st party games Sony pays the consortium BD royalties and it's given a small share of them back, while on 3rd party ones it doesn't pay anything and it receives its share of the royalties. The same applies to BD movies.
5) Like some pointed out, a new format could eventually become BD successor, but it should get through a similar path as BD is currently doing to achieve its goal, time needed can be different, but no format ever became mainstream just after release, DVD and CD took a lot of time, and while BD media adoption hasn't surpassed DVD market share yet, BD drives actually took less time than CD and DVD ones to become affordable. The next format could reach HW affordability even faster, but as BD already offers enough space to contain a long HD movie with extras in a single disc, and DD competition is becoming stronger, not to mention most producers wish to gather profits from it for a long enough time before jumping to the successor, next format could have even less and shorter problems on the HW front, but struggle more than BD on the format adoption one. The mix of pros and cons for next format is still very undefined and unpredictable and no physical format ever experienced the same mix as the others.
6) Multistandard drives able to read BD too, but using HD-DVD or a derivative for games could be a good solution for MS, and by 2013 its overprice compared to a plain BD drive should be minimal (although the discs, produced in a smaller scale than BD, would be a little more expensive, but not having to pay BD royalties on them and owning some of their patents instead should make up for that).
