I think at some point MS will inevitably enter the handheld division. But I think they're going to wait until the tech meets both 360 specs (bare minimal )and advanced peripheral specs.
Microsoft has been in the hardware game for 17 years now, why would they all of a sudden jump into the handheld market now?
360 specs for a portable is already a thing, Switch is a moderate upgrade over 360 and many smartphones tablets specs are greater than 360
Portable VR/AR already exists on smartphones/tablets.
Neither of these things are going to make an Xbox Portable sell well and since 1980 when Nintendo got into the handheld market with Game & Watch, only one out of dozens of competitors have been successful.
Microsoft releasing a handheld would be a terrible idea.
When the herd loses its way, the shepard must kill the bull that leads them astray.