Storage
SSD controllers are a real startup category. The flash underneath is a commodity from a small number of fabs, but the controller — wear levelling, error correction, the flash translation layer, the whole job of making a degrading medium look like a reliable block device — is where the engineering and the differentiation live, and it is tractable for a small team.
That job has been getting harder on purpose. As NAND scales down, density improves while endurance, latency and reliability all decline, so each generation hands the controller a more hostile medium than the last.
This lane is currently the thinnest in the registry. Deepening it is a priority alongside the HBM vertical.