To QuickBooks Online, Is there any update to this - ability to allocate more than one customer to a  Project?

"...I believe the only way to do this is by adding a dummy Customer that you project would be assigned to. And then add your clients as subcustomers of the Dummy customer..."

This looks like a workaround that does require more effort. Means we would end up with an extra :Dummy customer for every projects.

This solution is not that hard to implement.