Thanx for all the input. I can certainly see how adding extra curves in the cabling to route it inside the frame can add extra friction on the cable when braking or shifting. I'm sure that if it's done right, it shouldn't be unreasonably more though. At least not for my needs. I found a web page that gives some tips on cables to use that minimize the friction.

The extra weight it may add... I can't imagine it'd add enough to bother me. Maintenance looks like the biggie issue. I read a couple tips on how to run new lines and while it sounds simple on paper, I'm sure in practice it's a whole different thing! I think all in all... it won't be a must-have feature on my next bike, but it won't be a deal-killer either.