I know Sync for Android is being worked on, and I have heard that payments sync is also being considered for the future.
But I want to reiterate that Payments Sync across devices will be a killer feature for Brave and BAT.
Once implemented this will immediately boost the ease of use for Brave / BAT users and the utility for content creators / web hosts; the former will feed into the latter. For example, BAT already competes with Patreon (hence the interest with the YouTube channel tracking and payments) but Payments Sync across devices will significantly boost this feature; it would become compelling to stop using the YouTube app on mobile and just watch YouTube videos in-Brave-browser instead because of this greater utility for example.
This type of pseudo-identification via Payments Sync will obviously be incredibly useful once BAT is opened up to its advertising implementation.