This would be useful for the gigabit runs in my house that aren't quite up to spec. Usually it's a single pair that was damaged by a finishing contractor.
I did an Y-splice for three computers, without switch/hub, it worked.
I saw a damaged link with 50% loss on 3com 905 on the server end, RDP was unusable. Replaced with RTL8139 (other side was the same lost to time noname unmanaged switch) - less than 5% loss with ICMP ping. RDP worked fine.
Damaged a CAT-8 a little while ago, trying to pull it into my office.
The best future proofing thing you can do in a living house is lay down at least x2 cable per drop.
Not the best solution, and usually quite pricey, but it works. If your power cabling is not from 1900 too. *grin*