The problem is for anyone who sees prototype OO as a better solution. They kind of give their blessings to the other OO, which is a bit sad.
(edit: spelling)
Though the people who 'get' prototypes swear that they're the greatest paradigm ever you will still get a huge amount of people coming in from other languages which find the prototype chain awkward and prefer to think in complex class hierarchies.
These people who choose to create their abstractions out of classes are in no way 'wrong.' To each their own.
Adding `class` syntactic sugar is just standardizing on something which many people already do every day.