Most research on human embryonic stem cells - currently impossible in western countries due to ethics concerns.

Theoretically, if a few stem cells from every embryo early on and frozen that might be a huge boon for them once they grow up to adults with potential health issues. Need a new heart? Grow one in a lab from the preserved cells - perfectly compatible.

Currently these kinds of things can’t be explored, and whilst the ethics may be dubious the potential medical benefits left on the table are astonishing.