Since there seem to be threads asking for another Baldwin 4-4-0 between the IF and OF versions (both wonderful...I really don't see a need for another), and since I posted the picture of a Stearns Heisler several years ago when the Vulcan Duplex announcement was met with, shall we say, lukewarm appreciation...may I offer another humble suggestion.

Take about 1/2 of the On30 Mallet and give us a small catalog prairie

Here's a look at one left in New Jersey

http://www.steamlocomotive.info/onephoto.cfm?display=852

Seems to me that the mechanism already exists in the 2-6-6-2 undercarriage, and this would make a nice little addition to the line.  BTW the new Heisler looks GREAT!