>So the logical followup question might be: what's the most interesting
>work that Mahler never wrote? Any speculation?
I once started a thread which asked listers to suggest the work they
wished Composer X had written and there were some interesting ideas: I
floated Mahler's Piano Concerto and Mozart's Cello Concerto. It might
be long enough ago for it to be revived.
Incidentally, I thought that, had a violin concerto by Mahler been
genuine, one by Schmidt would have made a good coupling, and certainly
at first blush it made the CD seem authentic. A violin concerto does
not appear in Schmidt's worklist in Grove, and it seems a safe bet that
this work is as fictitious as the Mahler.