With ‘grpc client API’, someone can build an awesome module for MM someday. But I cannot wait.
So…
I opened IFTTT;

If [Google Assistant] to [Maker Webhooks]

If your home internet box can support DDNS(or static IP), you can make your mirror visible from outside your home by port-forwarding. It means IFTTT can send some message to your mirror.
I tested some message with MMM-IFTTT. it works.

So I made some IFTTT applets;

If you say “Wake up”, then make a web request ‘POST {message:‘screen on’}’
If you say “Let my mirror $ (or Tell my mirror $ or Ask my mirror $)”, then make a web request ‘POST {message:$}’
…

And I will make a small listener for the listening requests from IFTTT hook. The listener will parse requested commands and find proper MM notification or some function with my pre-defined mapping recipes.

It could be like this;
I say “Ok, Google. Let my mirror ‘sleep in ten minutes’”. Then, GA run in the background of my mirror listens that commands and IFTTT trigger will be fired. GA will response me “Yes, she will ‘sleep in ten minutes’”(response format could be defined in IFTTT).
And ‘sleep in ten minutes’ message will be posted to my MM via DDNS, and after parsing and mapping the message to turn display off.

I have no time because I’m just a holiday hobbist. So, I could make this real in this weekend. But I think it is very simple, therefore everybody can make his own easily.

Anyway, if you have not only DDNS but also SSL certificated server, it could be easier and better to make webhook directly without IFTTT.

I’m reading ‘grpc API’ all day long, It just gave me some headache. so I want to escape. I hope there will be someone who can provide the awsome native integrated GA to us.

ps. Alexa-IFTTT is not good as GA-IFTTT. Alexa cannot pick ‘ingredients’ up from your sentence. So if you use Alexa, you should make so many individual applets for all commands you wish.