So I can use my BR miles on NH upgrades?
Yes & no. Star Alliance does have a cross upgrade system, but requires an expensive base fare. So useless for most people.
UA thread on this topic (same principle for other airlines):-
How to upgrade with UA miles on Star Alliance carriers
Ah so I can use my Alaska FFP miles to upgrade a KE ticket?
No. My understanding is AS does not do cross airline upgrades.
Upgrades are never guaranteed. And far less common on non USA airlines compared to USA airlines.
Now days is common that low priced fares are not able to be upgraded. But does depend on the airline.
It seems I've kept my Alaska miles active through dumb luck..
Worth keeping the AS miles alive. AS is one of the better ffp's, but has a restrictive award chart.