Here are some ideas that would interest me:
Switch-barrel rifles:
e.g. Martini .22LR and .22 Magnum
Take-down rifles, perhaps even with multiple barrel sets (Notice a pattern here)
Stalking rifles (How about take-down switch barrel ones)
Quick-detach scopes, such as claw mounts, EAW swing mounts, Kreighoff slide-off mounts
Gauge rifles. How about a single-shot 12 bore on a Martini Large action with rifled barrel, heavy iron sights and set up for round balls. I have an extra Martini takedown GP shotgun if someone wants to install an ER Shaw rifled barrel and fit it up with good irons. I'll stock it just like a English stalking rifle. (Wow, since it already has a shotgun barrel, it would be a takedown rifle as well!)
Making fitted takedown gun cases. I've made a few in my time and may have a few in-process photos. I have one in the works now for a two-barrel shotgun.
