If an external add-on is allowed, I don't see why MS can't meet the desired performance level (should they choose to commit, of course). There are probably many ways to do it with additional hardware.
Assuming a "straight forward' implementation, the add-on would compete with standalone Blu-ray players with little differentiation (So price becomes a major decision factor, which is not good). They also need to keep up with any Blu-ray incompatibility issues (whatever is bothering BDA right now). At this point in time, there's not much incentive for MS to do so.
As for the future, we can talk about it when there are newer development.
I do agree that some third party might be interested to pursue the opportunity though.