The trouble with pretty much all of those ideas is not their suitability but our perennial friend, lack of a modeller. Crossbow units have suffered particularly from this, I know, and I'd like nothing more than to add Quarrellers and Dark Elf Crossbowmen, but I simply don't have the ability to do so. (For the uninitiated, a model in Rome Total War is made up of the "skin", basically a paint job, and the "model" underneath it. I can edit skins and we can do some pretty clever stuff with them, but I don't have model editing capabilities so the few bits of work we're getting done on that front we're relying on other mods' modellers generously giving up extra time. I've chosen the things they're working on pretty carefully, and if all goes to plan I think you'll agree I chose well.
)
So basically I'm finding things to do where I can re-use an existing model in a different/interesting way. I haven't got anything suitable for making leadbelchers or scrap wagons; gnoblar trappers are a possibility, I think. I had a go at Yheetees a while back but they looked pretty rubbish, gorgers are the other possibility but again I think they'd be hard to make look good.
Dragon Islanders... if I could do good dragon Ogres the beastmen would have them already. I'm thinking I might actually give them a medium human infantry unit.
Their current roster being:
Spearmen
Archers
Ballista
Farala Guards
Savages
Golems
Zoats
Part of the theme of the faction is a mix of semi-civilised and magical units (they're like Araby in a way, as being a human faction but with a strong elemental magic and monsters element), so I think maybe a sort of merchant guard inf unit or something could work. The other idea I had was an air elemental but that could be hell to make work well.