Up until now it hasn’t been possible due to the restrictive API. I’ve looked into the new shortcuts and Siri API docs and although the beta documentation is sparse, I’m confident I’ll be able to develop a natural, first class Siri integration.
Unfortunately, it won’t be trivial to implement (at least to do well). It probably won’t be done before the iOS 12 release, and I’m hesitant to start working it just yet due to the sparse beta docs.
Over the next year or two, I think there will be some great Siri integrations built. Hopefully, users discover and use them :)