I'm not going to say all bikes should have internal, but certainly I'll be specifically looking for internal cabling on every future road bike I buy. I can see how mechanics might dislike it since it takes a little longer to run the cables and they do it constantly, but for all of us, seriously? How many times do you change your cables?
I've redone cables on 4 of my bikes over the last 3 years (not always because I had to, some were simply upgrades), 2 external, 2 internal, and the difference in hassle is pretty small. It looks slick, it works perfectly, and costs me 20 minutes of extra time a year. I even just re-did my main bike with Di2 and running the electric wires inside the frame was a piece of cake. I'm just a random joe blow, not some mechanic. Not a rocket scientist. Heck if you BUY a bike already setup, then running new cables is dead simple...they'll even give you free sheaths to slip over the old cable before you remove it which will maintain the pathway for the new cable to go in. Once you're done, pull the sheath out, and you're good to go. If that extra 20 minutes once a year is a big deal to you, fair enough, stay external.
I get that it's not for everybody, but it's available, it works, and every time I carry my bike or wipe down the tubes without cables getting in the way I'm glad I've got it.