I am not sure that Juju should be changed to account for streams being out of date. The only way the suggested scenario can happen is when a new Ubuntu series is released and streams have not yet been updated. Our streams publication should be ahead of the curve and ensure that streams are always current. Juju clients will work with Ubuntu+1, so long as the streams contain that new series (IIANM)
I am not sure that Juju should be changed to account for streams being out of date. The only way the suggested scenario can happen is when a new Ubuntu series is released and streams have not yet been updated. Our streams publication should be ahead of the curve and ensure that streams are always current. Juju clients will work with Ubuntu+1, so long as the streams contain that new series (IIANM)