Most everything has its place. Scratch building to building from a quality kit or from a sub-arf to the PNP, it all depends on your wants and needs. Another "KEY" factor is if you have a place to build and not just on the kitchen table after the dishes are cleaned and put away. I'm very fortunate that I have a dedicated building shop and not just a corner of the garage. It makes building any of the above much more enjoyable if you can leave your project alone and come back to it as you can. Not to mention the dust and smells and noise associated with building. There's also the investment of modeling type power tools and such that can be a bit of an issue for some guys. If you are starting from scratch in putting together a shop it can be quite expensive, most of us builders have done this over many years of modeling. I for one love to build, so far. But I also see the merit in just picking up the phone and placing an order for an almost ready to fly or finish air frame in either prop or Jet. I'm also very fortunate to have two boys ages 11 and 16 that love modeling and flying R/C. We have the best father/son time in the shop and those are memories I will never forget, except when the eleven year old uses my CA like he is pouring syrup on a stack of pancakes at IHOP. If I leave any scraps of wood or fiberglass laying around he is gluing it to his next creation, kinda cool.
We do live in a "push a button want it now kind of world" and that is not what building is about, it just takes dedicating time to it and learning from others. To answer the question if building will ever come back, I don't think it has ever left. There are just less of us around willing or able to do it.