I'm with everyone on passive speakers internally. When you install the speakon wall plates definitely make sure they get specced with dust covers and that they are used and get replaced if broken.
For the stage cabling and such may I suggest something with a remote stage box(x/m32 with dl stage boxes) but the stage boxes remain in the cupboard with the amps. You then install 2-3 multicores to each stage with a weather-resistant multipin connector, something probably bayonet type with water and dust proof rating so that you can just move 2-3 drop snakes between the two stages and connect a network cable to the console.
What is happening for lighting at this time?
What's happening for power?
If they want to do this properly then maybe they should be looking at having a california(or something to code, I'm in another country) at each and have a house distro that they just move between the two stages?
Convenience costs money, this needs to be made clear to them. I really think you can find some passive boxes that will work well enough as a compromise in both venues yet still sound good. The speakon connectors just need to be well labeled and they will be at least mildly idiot proof(although I've met enough people who do not know how to connect/disconnect a speakon connector that I cannot guarantee that)
