I'm considering using MongoDB for some limited cases in our app:

1. A capped collection of responses from a 3rd party endpoint (XML) that we often want to go back up to 2 weeks and have a look at.

2. Data that is all reads after initial write: Historical data, lots of it (100-150M rows and growing fast), that we want to take advantage of the scaleout nature of MongoDB to handle.

3. "Built out data": Data that is the summarized output of the ground truth in our MySQL DB that is expensive to compute, has a varying JSON schema, and we want have ready at our fingertips for the frontend.

It seems like MongoDB is well suited for these use cases, leaving our transactional and user data in MySQL.

Am I crazy? Should I be considering one of the alternatives instead?