ReactJS (and possibly Redux) tooling
I would love to see some tooling surrounding ReactJS development. While I believe that on your competitors (Chrome/Firefox) these were developed by the community (or the vendor themselves...FB). I would love to see a CTA by Microsoft for this to be developed possibly following the example of Taylor Otwell surrounding his CTA to have Vue.js testing abilities added to the library.
Granted if Microsoft were to build the tools that would be amazing, but I don't think (in the day and age where Microsoft is so open source) that Microsoft calling on the community for a specific task should be ruled out.
So please either build ReactJS tools yourself or issue a call to action for the community (or FB directly)!