The object of Xbox Cloud Gaming is to make Xbox games more accessible by bringing them to a wider variety of devices. Asobo Studio confirmed mouse and keyboard support is coming to Xbox Cloud Gaming in an interview last week. There is no firm date on the feature, but it's certainly coming. The Microsoft Flight Simulator developer held a long Q&A last week (watch below), right after the flight sim became available on Xbox Cloud.
Flight Simulator head Jorg Neumann started talking about the cloud version of the game along with mouse and keyboard support around eight and a half minutes in.
Neumann said it's a platform-level feature, so mouse and keyboard on the cloud will work with more than just Flight Simulator. Xbox Cloud Gaming already supports touch controls for some games because not everyone using a mobile device has a controller (Microsoft doesn't limit controller support to Xbox controllers). By the same token, not everyone streaming games on PC has a controller.
It's interesting to consider how this would apply across Microsoft's selection of cloud games.
The games with PC versions may simply switch to their PC control schemes, or they may not since the cloud servers are running on custom Xboxes. Players may simply be able to configure keys to correspond with Xbox controller buttons. Would the cloud add mouse aiming to a first person shooter that has never had a PC version?