Provide clear support statement for SPFx with IE
Right now there is no clear statement regarding the supportability of IE with SPFx. Since IE 11 is still supported for O365 and SharePoint Online, customers assume that it is supported with IE as well.
Currently SPFx is impossible to use with IE because of performance issues and very bad memory leaks in IE. The more content and web parts are on a modern page the worse it gets. Thus, I suggest that you either fix those issues, or make a clear statement that SPFx is not supported with IE anymore. This would really help customers in making their decisions.
I have heard recently that the team is wrapping up SPFx development and moving towards efficiency improvements and finalising the framework and tooling.
We have found that we can keep IE happy if pages are kept to as few web-parts as possible and to advise clients to use modern browsers where possible.
This is an issue inherent to modern stateful frameworks and IE will always be an issue here. They certainly can make improvements to SPFx but I very much doubt it's possible to get parity between a modern browser and IE11. We seem to experience ~4second render time for IE11 in a fairly populated modern page. Not great but our clients can survive if they're adament on using IE11.