Comment by rfc

Modular housing that grows with your life. Biggest problem there is effective expansion joints that would hold the houses together.

Affordable container ship that is electric.

A personal finance software that solves upper-middle class issues (eg. primary income, side business, rentals, etc.).

A product/service that makes CROs obsolete in drug development (CROs = 25% of cost of drugs; admin overhead)

Idk, those are some that immediately come to my mind.