I share somewhat, Kyle's concerns at having the DD two-fer built into the raceway, as it severely limits (pretty much prohibits the use of and) the flexibility of the system to use fixtures other then those accepting 77v lamps.
That said, I think the fault lies with the consultant and/or architect that allowed this in the first place. For all we know there was a Project Manager at ETC who has a 'puter hard disk full of e-mails stating that it's not the best idea in most instances. At some point the manufacturer is going to build what the consultant spec's, or lose the project, as well as potentially future projects down the road. That's probably not good business practice and in truth has anybody ever heard of permanent DD systems prior to this ?. I never knew it was an option, not that I'd go that route anyway.
I am also not a fan of DD in permanent facilities in general, feeling that the need to keep track of A and B sides to a dimmer when patching, dealing with visiting consoles, etc... make them a pain to deal with.
I have to agree with SteveB here..this sounds like a descion made outside of the ETC family. Someone thought it was a "smart" way to save and didn't plan for every eventuality.