After showing up in the N developer previews last year and being removed before final N release, mouse capture without root is back in Android O.
This means that device running O will be able to use a mouse without the cursor desyncing from the host. It also means that when Chromebooks receive the Android O app runtime, mouse capture will work on those devices too
Hopefully the API survives DP3 this time (when APIs are finalized).
Update: Not only has it survived API finalization this time around, the implementation works like a charm! Once this version hits the Play Store, the rooted version will no longer appear in the Play Store for devices running Android O. The non-rooted version on O will have equivalent functionality with no root required.
Update 2: It's live on the Play Store in v5.1 and later.