Well that would be very interesting... if also a little strange.
It would do nothing for Microsoft and it would only give them additional financial headaches.
It is clearly observable from the period when Sony had an exclusive F1 licence that it didn't pay off from them. And we are speaking about the license obtained during the PS2 golden-age, with insane market cap that PS2 had during the period (2001-2005 era).
FOM simply have very hardcore terms and they ask serious money for their license. They have influence over game-design, usage of assets and all teams are involved into decision making through FOM partnership. It is apparently very demanding to meet all their expectations and terms.
I could imagine that Microsoft would be interested to obtain F1 license in order to incorporate the F1 into Forza, it would be only viable solution from point of costs of development, marketing and actual license. But I am not sure can such thing happen due to FOM terms, aka, can the F1 game even exist without being standalone.
I have never read such rumour before, but it could be possible that Microsoft is chasing it - they certainly can afford aforementioned 15$M annualy to Bernie, but the question remains what do you do once you secure the license.
After great results Sony had with critically acclaimed F12001 and F12002, sales simply fell down the cliff, because it is hard to keep high sales for the annual title that does not significantly improve - all of us that are F1 games fans here (and we are buying all F1 games) would probably agree there is actually not much difference among annual titles in past series. And locking it to only one platform simply does not work. Nor will work in the future, it is simply non-sustainable model.
In my opinion, it would be best if FOM would decide to allow multi-licences (as they were during 1990-2000) period and to give all interested studios an oportunity to build their best possible F1 game. And then to let market decide which one is best. However, I am also aware that current cost of developement of F1 title from the scratch would be gargantous for AAA market.
Online service model would be best, but it is not a subject for this discussion.
But if Microsoft license F1 and deal becomes a reality, it will be very interesting to see what they can do with it. In the past 15 years noone was able to make the license commercialy work for longer than 2 years (including Sony).