I'll second Dave's comments on a 1:20.3 version of the On30 2-cylinder Shay; I have an Accucraft live-steam

one, but with uninsulated drivers, it doesn't "play nice"

with the track-powered, DCC controlled Bachmann locos (Accucraft DID do an electric version, but being a brass loco, it was as pricey as the live steamer!)

. For a larger prototype, a 1:20.3 3-truck Williamette would be nice (although I'm not sure if any 3-foot gauge prototypes of the Williamette actually existed). A Little River 2-4-4-2 Mallet would also be an interesting prototype.
I can certainly understand why Bachmann may be getting into 1:29th as well; I occasionally change time period on my "Watuppa Railway" and run 1950's New Haven prototypes. I'm also a Pennsy fan & one steam prototype which would probably sell VERY well would be a PRR K4s (especially if multiple prototypes were produced such as Bachmann has done with the K-27; a "classic" 1930's K4s with the "chicken coop" pilot

, a 1950's version with the so-called "beauty treatment"

with the reversed turbogenerator & headlight positions, and cast pilot with drop coupler). There are also plenty of diesel prototypes which the the existing 1:29 manufacturers have not produced (I'd be a potential customer for a New Haven Alco RS-11, for example). And one VERY modern prototype Bachmann already produces in N & HO - the Acela!

(As far as I'm concerned, the LGB "Acela" - a relettered German ICE with STICKERS for windows!

- was a joke!). I think a Large-Scale 1:29 Acela, done to a level of detail comparable to the fantastic Spectrum Large-Scale long Rio Grande caboose, would be a fantastic piece of modern equipment.

Just my 2 cents. worth.

Tom