About the latest Duo-Art I know of is a 1936 Weber.  It's one of the
fan systems that Aeolian produced as early as 1927.  Mostly these fan
systems seem to have been intended for use with the Concertolas, but
they do also appear in some really fine pianos.  There were a number
of Steinways built in the late 1920s, one of which is 9'6".

The fan system does not seem to have been meant to have replaced the
standard system Duo-Art: there are a number of 1935/36 Chickering
Duo-Arts with the standard system in them.  The fan system could have
easily been installed in spinets but as yet nothing like that has
surfaced.  But who knows.

Bruce Grimes