I'm not sure I understand how your design overcomes the issues of either type of database. You'll have unstructured data like a NoSQL database by virtue of your

I'm not sure I understand how your design overcomes the issues of either type of database. You'll have unstructured data like a NoSQL database by virtue of your insertion mechanism, and there is no mention of how you plan to optimize for record size the orders of magnitude that would be required to keep all data in memory. As a thought exercise, say my average record takes up 1Kb. After only a few million records, with zero overhead for the database structures themselves (not to mention unrelated processes also runnin on the system) you've already exceeded the amount of memory typically used to run these types of processes.