How about giving top tier mason access to
http://wiki.sk89q.com/wiki/CraftBook/Minecart_control_blocks#Stations
This would allow us to further accent the towns or areas that we work in with nice aesthetically pleasing rail systems. This could open up the possibility of towns connecting themselves with a public rail system. With the further possibility of being able to charge for travel maybe??
While I like your idea, unless you can find a way to make for example stone bricks act and behave like obsidian without looking like obsidian, having all my "reinforced blocks" look like obsidian is not ideal and i can see this leading to everyone building region walls with the same material and all looking the same and ugly.
I don't feel my suggestion above with detract from the server at all, and since it used limited redstone it shouldn't impact on server performance very much if at all, due to each control block only being triggered once when used and not constantly in use.
Well thats my thoughts, to expand the class and use a plugin we already have on the server, and not add to the hundreds you already maintain
As an addition to this, since there are quite a few options available to the control blocks side of the plugin, additional control blocks could be added in earlier, with the more popular ones like, station and collector/Depositor being held for the lvl 60 mason's.