That’s quite an unusual requirement, I imagine most people would consider those sites different projects. Unless you want the development server to have them all on one VM/Trellis, but in production you want them split across multiple servers? I’m just spitballing here, but using git submodules (pet love of mine) for the sites and trellis might solve that case.
The above topic seems pretty relevant for you too, though I’ve never tried a config like the one mentioned.