Now that the 360 is more than a decade old and has become basically irrelevant in the software marketplace, it may be actually feasible to bring some of their old, 1st-party 360 exclusives to the new-gen and recoup some extra profit.
I don't think their ability to profit off a port was ever in doubt. Actually I think pretty much any port of pretty much any game to pretty much any system that's an ongoing concern is going to be revenue-positive. I think the bigger issue is ROI: $10,000,000 isn't a lot of money when it means tying up staff and producers. Microsoft downsized their 1st party producer stable significantly at the beginning of the gen (transitioning away from assigning MGS producers to every indie game to ID@XBOX accounts for much of this reduction). It's notable that Microsoft has been among publishers that have done the least PC porting and haven't done any late ports of catalogue titles.
Hell, Fable 3 (which I think sold upper 6-figures or lower 7 on PC) ran out of keys and Microsoft couldn't even allocate a programmer to remove GFWL and put the game back on sale.
I also think with MS, the divided loyalty internally between actually supporting their software and using their software in a vain effort to push dead-end storefronts like the Windows 10 App Store is still a problem. We saw it with Windows 7, where they published quality first-party game apps and deliberately didn't release them on iOS or Android where they would actually sell. Later on they partially changed their tune, but with the release of Windows 10 and Windows Phone 10 devices they seem back on the bandwagon that they should be willing to sacrifice their software to push their platforms. I think that's a bad trade personally but it seems to be where they'd be.
I think the question of whether or not they will continue releasing
any software on Steam is a more manageable one than whether they'll greenlight new software specifically to take advantage of the Steam long tail.