Not many hobbyists are building cd players for instance.

Many have made turntables.

At a DIY show do the builders of product which is discussed
in the forums here then exhibit their latest creations looking
toward acceptance and sale in the marketplace?

For this a yes or no will do.

Or should a DIY show feature one-off builds by hobbyists
exclusively? This would apply to SET amps, speaks, pre's
etc. And do kits count?