It's not easy to support npm in Construct as it runs in the browser without any involvement of node. If you can get a library you want packaged in a manner suitable for using in a browser, it should work in Construct too. So usually the trick is to find some browser-compatible package of a library.
Is it possible to support npm in the future? The number of SDKs (social media integrations, ..etc) increase every day and it is not feasible to ask the C3 team for plugin for each sdk.
My main focus is HTML5 games.