First stab at it---no more "handcuffing"
When star players get hurt, the owner of that player should have first dibs on the respective backup. Here is an example/scenario of what I am advocating. RB Alvin Kamara gets hurt and is put on IR. The owner of Kamara should have first dubs at RB Mark Ingram--Kamara's backup. In the real world, the coach of the Saints just inserts and starts playing Ingram. There is no scrambling to fill the hole created by the injury. So, if the owner of Kamara wants to add Ingram, s/he should be offered first dibs at Ingram. If that respective owner passes on Ingram, then, and only then, put Ingram on the waiver wire for the rest of the league's owners. So many times an injury can cripple the advancement of a team who are "in a zone." I believe my idea is more realistic and helps a team owner who just lost a big star remain competitive.
Derek Patterson commented
So you want Yahoo to cover for you because you didn't think ahead?
Really bad idea. You are asking Yahoo to murder the whole purpose of fantasy sports: scout, target, acquire.
What you suggest is something better left off for non-superfan casual leagues.
Glen McLaughlin commented
Here's why this is a terrible idea. Using this same example, if I drafted Alvin Kamara and didn't have the foresight to draft Ingram as well, that should 100% be my fault. Fantasy football is all about taking risks and seeing things others don't. There would be just an absurd amount of roster shuffling to make this work. A common top pick in my leagues was LeVeon Bell. I drafted James Connor in the late rounds of both of my leagues. Great foresight by me, as it turns out. If your method was implemented, would Connor just be plucked off of my roster to give to the guy who drafted Bell? Who would I be given to make up for that lost production? I guarantee whoever it was wouldn't match what I lost. So while injuries suck, you have to plan ahead. Keep a low level starter, a project guy, or have the smarts to take a handcuff. You have to hedge your bets. If you go all in on one guy and it doesn't pan out, that's on you.