I have been working with WebAssembly for at least 1 entire month into getting my entire Game Engine and DRuntime ported to it. As I'm almost reaching the point of the new announcement, I come here to show how I've done DUB's dependency compatibility with a custom runtime.
The way to use dub's packages is by using the DFLAGS. With DFLAGS, I can set the import path to my own DRuntime and own std. That way I can make the dependencies behave more or less the same, this is an example of what is being done now:
set DFLAGS=-I=%HIPREME_ENGINE%/modules/d_std/source ^ -I=%HIPREME_ENGINE%/build/wasm/runtime/webassembly/arsd-webassembly ^ -preview=shortenedMethods ^ -L-allow-undefined ^ -fvisibility=hidden ^ -d-version=CarelessAlocation dub build --build=debug -c wasm --arch=wasm32-unknown-unknown-wasm
So, when dub tried to build their dependencies, your custom runtime overrides D's default ones. In that case I'm overriding both D std and D core/** and object.d
Keep in mind that you'll probably need to setup some env variables such as mine done for making your script a little more portable to other developer's PCs. I would really like if there was a way to define global dflags on dub though.