Single Comment

The problem is that if two games are too different, there is really nothing
gained by having them handled by the same GUI. You would basically get two
completely independent programs, that are both put in the same executable,
one of them serving no other purpose than occupying space while the other
is running. Tht becomes progressively worse if you want to handle more
unrelated games. They will each need their own code for game notation, for
parsing games, for describing moves, for performing moves on the screen.

For Chess variants it is very useful that they are all handed by WinBoard.
Most of the time the fact that you play a variant merely means the
parameters for the board format have to be adapted, and a few pieces are
replaced by a few others. With a limited set of unorthodox pieces a far
greater number of variants is automatically supported.

Of course you could make a client that is completely dumb, and does
nothing more than record mouse clicks and send tose to the server, and
display the board as a table of bitmap pictures, where it gets sent a
completely new boarad position (adapting the contents of every cell of the
table) when anything changes. And when the user asks to save the game,
relay the request and have the server send a text string that represents
the game, and save that. But I would not consider such a simple thing a
GUI.