I think it makes sense to formally drop the IE dependency in versions sooner than when you’re making changes that actually break IE.

Besides, replacing jquery May indeed be why they chose to drop IE right now. One of the biggest selling points of jquery, and one of the biggest contributors to its heaviness, is cross browser support including IE.

As one of the comments in the linked issue points out, dropping IE11 means they can also start using basic JS constructs, like Array.prototype.forEach.