I have been using Meteor, almost exclusively, on my projects for over 4 years now. Have loved it from the start! So I agree with @msavin, not much needs to change.
One wish list item however: a recent (client only) project I inherited worked with Parcel as a build tool. The build times are really lightning fast (often < 1s), and the client displays the changes right away, without having to reload. I found this was bliss for development speed and experience. It really makes a huge difference. And it’s almost that magic feeling I got the first time I used Meteor 
(although Parcel does have its issues; sometimes I still have to refresh or even restart manually to see my changes).
It would be so awesome to have this kind of tech in Meteor as well! A hot code reload without a refresh. Kind of how style changes already work in Meteor (although even these are still slower than Parcel build times). Normally, I would accept the argument that this is hard/impossible to do in a general-purpose framework like Meteor, or without a lot of configuration like Webpack requires. However, Parcel has 0 configuration, it works with React etc, and even automatically detects and installs build packages that are needed (e.g. it will install and run LESS if it encounters a .less file in your code).
Could this technically be done in the Meteor build tool?