With Microsoft looking to bring "console quality" streaming to phones and tablets with Project xCloud, how will the company achieve that when touch controls are still pretty bad? It seems the company is looking to bring physical controllers to mobile devices to offset this problem, according to these Microsoft Research papers.
https://www.windowscentral.com/microsoft-research-prototyping-xbox-controllers-phones-and-tablets
The work was carried out quite a while ago, back in 2014, but it seems Microsoft Research has resurfaced their efforts recently, noting the recent success of the Nintendo Switch.
Source: Windows Central
Seems they are getting ready for Project xCloud.