Canary nest

Muriel reading Aziraphale's diary is a cute thought. Them reading Aziraphale's depiction of Armageddon't and finding out about body switch, while still being loyal to Heaven (and they are loyal to Heaven at the point of S2 final), on the other hand?....

Not so much, I'm afraid.

I don’t think Metatron left Muriel on Earth just “to take care of the bookshop”.  But why exactly?

To keep a low-ranking angel knowing about Gabriel’s story on Earth? Or to keep tabs on Crowley?

They are terrible at being a spy, but they already have…well, not a friendship, but still some sort of non-hostile relationship with Crowley, and Crowley finds them amusing and non-dangerous (and if Metatron knows about Crowley’s trip to Heaven, he should know it); yet they still are actually loyal to Heaven. And Metatron considers them to be “dim”. Can it be that he wants to use it for his own convenience?

We all are imagining sweet scenarios where Crowley looks after Muriel while they are learning about life on Earth and they eventually become friends, but what if this exactly what Metatron wants? So he could fool Muriel into reporting to him about Crowley’s movements?

I don’t think it would work as intended - it’s dangerous to underestimate the “dim ones”. But can it be Metatron’s initial plan?

...Muriel probably could see The Confession through the window. I think it was already established in the fandom.

But also - they were with Metatron at the moment, who had to explain them their new appointment (I wonder, in what words?) while also watching the drama unfold through the same window.

I wonder if Muriel can say something...interesting about it. I don't know what exactly - the very fact he was watching (though if it would be told to Crowley in S3, he probably already deduced it?)? Some of his expressions or words - could he be a bit careless with them while being around "a dim one"?

Was there a reason Muriel was a bit sad in the bg when Metatron entered the shop after Crowley leaving it? Can they provide some unexpected (even to viewers) view of what they saw through the window?

....or maybe they just spent all their time reading and were sad because Metatron said to them it's time to start their new responsibilities and put the book aside. That's possible too.