With the tech we're talking about, there are definitely limits per inch. They'll be able to fit a petabyte in a 2.5" SSD drive case before the SSD sunsets, at a cost of $300. At that time, your 100tb SSD might be $50 to $75.
After SSD, what technology will take us to 100pb drives at $300? Is that even possible, while keeping the small size of the drive? No idea. It's going to require some amazing breakthroughs.
DNA storage[1]? It will be very interesting to watch computers become more "organic" over time. DNA for storage, processors that are correct "most of the time", deeper and more broad neural networks, etc.
After SSD, what technology will take us to 100pb drives at $300? Is that even possible, while keeping the small size of the drive? No idea. It's going to require some amazing breakthroughs.