Sort:  

The new Muse chain will look at BTC private keys (of the pre-sale) and current/old Muse private keys (or wallet file).

So those that only participated in the pre-sale with BTC and never claimed anything can wait for the new Muse chain to launch.
those that already claimed their stake and have MUSE on the current/old chain will have to import those Muse keys into the new chain's GUI.
Those that have their funds on BitShares/OpenLedger need to send them to the current Muse wallet. Those are the keys you'll need to import in the upcoming Blockchain's GUI.