There are biotech startups working on all of those already

There are a couple interesting gene therapy companies workout on hearing (akuous and decibel among others). Lots of ophthalmology gene therapy companies also, as well as more traditional companies. Hair regeneration has been a popular area of research for a while

Most companies work on biomarkers as part of the drug dev process. However building a business around just biomarkers is hard -- you need to develop your own drugs based on those biomarkers. Diagnostics is really tough bc reimbursement and pop health is tough bc incentive alignment is nearly impossible in many contexts