Pianos were never tuned in "the old, unequal temperament"--the modern systems of temperament were developed to make the piano possible(ungodly and untunable monster that it is)--

A lot of people don't realize it, but but string players play in what is pretty much "natural" intonation--when you listen to a piano concerto, the piano always sounds out of tune with the orchestra, and it is--most other instruments end up being in tune because the players adjust the pitch of each note a bit to make it fit--even though the guitar is tempered, we tend to squeeze those notes back to the natural pitch without even thinking about it--