Just wondering what the deal is with this. Are current Di2 frames just pre-drilled in the correct locations for the user to route the wiring themselves, or is there actually wiring already installed inside the tubing? I'm just trying to get an idea of whether or not a current Di2 specific frame would be desirable or useless if I'm planning on purchasing Ultegra Di2 in the near future.

Thanks!

No frame right now is going to be di2 specific for the most part. not unless you're a pro anyways. If you go onto trek's project one site you can see that they use the same sets of internal cable routing holes for all different group sets. Since standard groups and dura ace di2 have the same number of cords all the holes get used up properly. With ultegra di2 there's less cabling so you'll see that they just leave on cable router empty because its not needed. It's hard to tell but I'd imagine they have some sort of rubber plug for that hold to smooth it off.