I have a quick query; on 1 April 2014 when US leave *A .... does this mean from the same date, we'd be able to use remaining US miles and book onto OW (via AA)? Or will there be a transition period where remaining US points will remain in limbo in the sense that you can't book anything other than actual US or AA flights until AA/US sort their stuff out.
From the info we have so far and assuming no more announcements of the sort, the guess is that from 1 April, US will leave the Star Alliance.
At that moment, US DM will remain and similarly your US DM miles. You won't be able to redeem your miles for oneworld carriers, except for AA. You will be able to use your US DM miles to redeem for US flights, as well as select partners who are from Star Alliance (as listed in a previous announcement). At the moment, US, Partners and AA use different US DM charts, so you can't have AA and Partners in the same booking. (The last one is my hunch).
That is my guess from what's going on as well as based on US's announcements. What is lacking before you can use US DM miles for oneworld travel is:
(a) US formally joining oneworld
(b) Either redemption charts for oneworld partners (or recognition of oneworld carriers to use the Partner chart),
or a conversion scheme to move US DM miles to the AAdvantage programme.
In any of the scenarios in (b), it is not entirely out of the question that redemption rules may change (viz. redemption prices, routing rules)
Happy to be corrected on the points above. The only thing that seems certain is that come 1 April, there will be no redemptions on oneworld partners straight away with US DM miles, so the trigger happy wanting to grab those CX awards will have to be patient