Well it surely can be developed.. a model for mongodb and then make the GC Connect to Mongo ..
but with mongo beneath the layer, GC cannot be technically used for the same. for the following reasons that i forsee:
1. RDBMS like MySQL is structured... Mongo is (though structured but ) is more likely to be considered
2. RDBMS have data types defined. The same is not available with Mongo db.
3. There are Relations that can be explored in RDBMS / The same will not be possible with mongo db.
There are many such possible aspects that can come in line with when integrating the outcome with Mongo DB or any such no-sql dbs.
Biggest question that arise for me is.. what are you going to do about nested data sets in each row that a mongo db allows for storage? How is the same going to be handled? If you have thoughts on such questions, it is going to be great to have a wrapper / layer built over no-sql db sets.
There is a specific purpose as to how the data is going to be stored down the line inside Mongo DB .. for each row. A few shall be array .. and few shall be string. How are you planning to manage the add / edit functionalities around the same?
Such are many such queries / questions that keep a developer thinking before he can come to a viable solution.
I believe you surely will be able to work around on the same. Hoping for the best..
Happy GCing :)