I'm on the VS Code team. We did an initial investigation into what we would need to do to make this happen last week. It's definitely on the roadmap, more updates should come soon https://github.com/Microsoft/vscode/issues/396#issuecomment-...
Unfortunately there's quite a bit to get done because everything was built around the assumption there would only ever be a single folder. In the meantime I recommend Git Project Manager, which is what I use personally to deal with multiple projects https://marketplace.visualstudio.com/items?itemName=felipeca...