In the exact scale line, let's see, your already coming out with the P-51B/C Birdcage model so the next ones on the list would be (in no particular order);
[ul][*] BF-109E (lots of colour schemes available!)[*] P-39 Aircobra[*] IL2M3 Sturmovik[*] Hellcat[*] Ki-61 Hein[*] TBM Avenger[*] Dauntless[*] P-38[*] Ju-87D[*] LA-7[*] Maybe a Zero or Oscar
[/ul]
I think that if you offered each kit in a variety of sizes, like Wingspan Models is doing with their B-17, you would hit most of the market. While I like the idea of the nearly 1/4 scale P-51B, I think most people would be interested in something around the 1/5 scale for transport reasons. I also think that in picking the scale sizes, make them 1/4, 1/5, 1/6 etc., not 1/4.3 or 1/5.7, and make that uniform across the line. In choosing the scales you may consider some of the popular engine sizes like 50 and 85 cc.
The 1/5 and 1/6 size birds have a lot of accessories on the market, even the GI Joe pilots, and a 1/6 scale fighter would appeal to those folks switching to electric.
As far as kit materials, laser cut wood and maybe some available fiberglass fuselages are both good ideas you have.
Edited to add:
Oh, and try and keep accessory prices reasonable, I think wingspan will have issues with the $3900.00 retract price for the 1/6 scale bomber.
