Can Meteor take over Express in future?

You're comparing two completely different things

No, meteor is an all round solution not just an web server. It has tons of node plugins and layers, I see it like a dev environment, because the build is actually a node app.

As a side note meteor is too proprietary, I worked with it and wouldn't recommend use it except in a Hackathon or MVP prototype. The dependency is too high and vendor locking, and your project is successfully you end up rewriting lot of parts or pay a lot more or managed meteor hosting.

Like the others said,
Meteor is a Full Stack Platform which means that
it includes not only Express but also Front-End Framework Container (such as Vue.js / React.js, basically blaze.js), Back-End Container (Node.js itself) and especially includes MongoDB initially when it's installed.

And there's already a lot of library, something like web socket based method/call communication protocol(DDP), full reactive publication/subscription so you can program realtime things and so on.

You can use all the npm packages freely in Meteor,
and the best part is,
these everything is mixed up simple and clearly on the project,
so you can keep the each tech and replace as well as you need.

So simply I think we can say,
Meteor includes Express and so on.

I'm wondering too.