My friend, have you ever heard of the little something called a config file? If this machine were ever implemented, server hosts would more than likely be able to turn it off. Also, if you are trying to break someone out of a spawn jail.
A. if the jail is in fact, in spawn, you cannot place any blocks so what is the point?
B. If the jail isn't in spawn it would take roughly two days AT LEAST to break both pieces of bedrock (not to mention the EU it would take to do so). I think an admin would notice the attempted escape within that time.
C. If this person was jailed using a command it probably means that the server has a jail plugin. Meaning the jail would most likely be unbreakable even if it was made out of dirt
D. If the person who is in the spawn jail is a griefer, why is he in a spawn jail and not banned?
Consider these things.
removing Bedrock, which is not at 0 or max layer nor adjacent to the End-to-World-Portal-Block is maybe good for some buildingprojects, BUT on a server it is still a very bad Idea to break bedrock, which is for example used as Spawnjail (All the Griefers can get out of it, if they can find someone who releases them!!!).