Spielberg may already be lining up the next (and probably last) part of the Indiana Jones story. With cystal skulls just gone it would be wise to go sooner than later on the final chapter in Indy's career.
Rumours that Shia Labouf will take over seem just that, rumours. Still, with all those previous fake titles for the lat film maybe they had a few stories ready to go and who knows, it may be one of them.