Here's a very unethical linguistics experiment that I think would be interesting:
Raising a group of children completely isolated from any language, spoken or otherwise. They would not be fully isolated from people, but those people would not be able to communicate with each other in the vicinity of the children (no speaking, no gestures, etc.) Of course, to isolate them from language would mean strictly controlling their lives (very unethical). Could they communicate with each other, and maybe even develop a language?
Well that seems very unethical.
About gene modification, assuming it were to fully work without risks, it would still only be ethical if the patient were to consent, which not everyone would.