I'm doing this locally and it seems to work well:

// get a package with module typings
npm i my-module-with-typing
typing i npm~some-module

// custom-typings/my-module-with-typing.d.ts
export * from 'my-module-with-typings'
export as namespace MyModuleWithTypings

// custom-typings/some-module
export * from 'some-module'
export as namespace SomeModule

Maybe typings can create those custom typings files directly?
In this case, we can reduce the registry by half.

Of course, one issue is how to determine the module's namespace.
How will DT do it for @types?

Lately, I'm working on globalify and released my own @unional/globalify which I can define my own global namespace variable.
It can help but still need to deal with libraries that already release global umd build with special namespace variable.