I work as a teacher and have some pupils who vandalizes and some who contributes. Therefore the schools ip-address needs to be blocked and as some who vandalizes when they get blocked simply creates an account and continues, the account creation must also then be blocked. Those who contributes will very rarely create their accounts elsewhere and later make their edits and therefor account creation should be allowed.
However, as the threshold to vandalize is higher if you need to create an account first few would do that and a simple solution would be to have a short total block and a longer block of the ip-number but then account creation should be allowed.
There is no easy solution to this as a sysop needs to change the block after a certain time. Therefor I request that it should be possible to let the system be configured to automatically block account creation for some time and then a total account creation block would very rarely be necessary.