Some form of piano rebuilding started soon after pianos came into being in 1707. With the advent of steel and cast iron plates in the 1800's, high-tension scaling meant that pianos in places like New England came to need soundboard repairs, new pinblocks, and restringing.
During the 70's and 80's here in Boston, there were a lot of pianos dying. They first stopped being tunable, which meant tapped tuning pins (until you could not tap them any further), pin tightening fluid (until its mess and ineffectuality discredited it), or a new pinblock. In the early part of this period, most soundboards were repaired and shimmed. But even as the techniques for this approach were being mastered, rebuilders started opting for the more predictable results of soundboard replacement.
In the 1970s and 1980s, a large number of upright pianos exchanged hands, many receiving some restoration, but by the 1990's, the market fell out from under the affordable upright.
During this time, many lesser-known makes of grand piano received degrees of rebuilding. Henry F. Miller, Steiff, Vose, Steinert, Chickering, Ivers & Pond, Hardman & Peck, Weber, Knabe, Baldwin, Sohmer, and Hallet & Davis are names that come to mind. An almost-viable market burgeoned until new Yamaha, Kawai, and other imported instruments became more popular options in the same price range. Now, the rebuilding trade (at least in the Boston area) largely concentrates on Steinways, Mason & Hamlins, and various European makes.
It should be noted that sentimental value, particularly for pianos passed down through the generations of a family, can trump marketplace considerations. And these pianos may not be Steinways, but they can be great instruments, with beautiful cases and musical voices.