Vacuum tubes continued to be improved all the way up into the early 1960s, long after transistors had taken hold:
https://en.wikipedia.org/wiki/Compactron
One in particular was used mainly in television sets, all the way up into the early 1970s:
https://en.wikipedia.org/wiki/Nuvistor
...it competed with transistors, and was almost as small as some of its contemporary transistor cousins.
Even today, you can't rule out the vacuum tube - for some things, there isn't any substitutes:
http://www.nutsvolts.com/magazine/article/vacuum-tubes-for-t...
...and new ideas for the old technology are being investigated:
Even if by chance neural/deep-nets stop being the primary source of AI innovation, I'm sure people will find and make improvements in them regardless.
I'm not saying gluing bunches of deep nets together is bad R&D, only that it may not be the only or best AI game in town. I suppose if we got a wad of deep nets to give General Intelligence (including "common sense"), but it took a big room of servers, that may be a good enough springboard, but I'm not sure putting all our eggs in the deep net basket is the best route to fuller AI just because it's been the most promising up to this point.
It's roughly comparable to spending all R&D perfecting vacuum tubes in the 1940's because they were the best known route back then to general digital electronics. The best starters are not always the best finishers.