I'm truly in a mixed bag on this suggestion.
It is a good suggestion and would be extremely helpful in maps such as Underjail and Crossroads, where you can shoot through (!) the celldoors. As persons said "the rounds over before it even began".
To have this added would eliminate the problem of this.
However, there are (unlikely) scenario's as well where this would be not a good suggestion. I'm giving examples such as Minecraft and Oranger maps where you can escape into the breakable.
It takes a while to get to the warden at first as a rebeller. But if you escape the breakable and reach and kill the warden in time before the cells even opened, then it would be sad if someone can rewarden because that's just a impressive rebel.
Personally I would like to have this rule only apply for certain maps. But at the same time I can see that it will create massive confusion in the process and we already have a lot of rules to think about.
If by chance it is acceptable that it can only apply to certain maps, then I'm fully on board with this. But I'm voting no due to the unlikely scenario's I described.