New motivation

[lilnasy]

After an early implementation of it broke websites, the proposal for array grouping is switching from Array.prototype.group (instance method) to Array.group (static method). The sentiment expressed by implementers is that they don't want to keep extending prototypes, and hoping it doesn't break the web.

This signals that method chaining will become less and less viable over the next decade. It might be worth it to add this to the explainer as a motivation once grouping reaches stage 3 again.