I like where you're coming from, @James Cutts - now that you mention it, the pikes thing seems to be well-suited to army-builder sets, as it seems to me it's not likely you'll need a big variety of poses and weapons variations. Maybe some variations in helmets might be needed, and certainly the pikes would need to be separate from the bodies for manufacturing and packaging reasons (as opposed to the Prussian set, where both arms seem to be sculpted on the body), so I would imagine the army builder set would contain fewer figures just by the nature of the thing (polearms and spears seem to take up a lot of sprue real-estate!), but it seems do-able as an army builder to me, and more practical that way.
I'm leaning toward a "Cold War" line as something I could make the most use of, but to tell the truth, there's a lot of fun subjects covered by that poll, and it's not an easy choice.
I kind of thought of the Hundred Years War as being early Renaissance, and would have been just as cool seeing that as part of that existing line, but either way, seems like a fascinating period, and something I'd be more inclined to turn to for Classic Fantasy human figures in general, along with Conquistadors.
The American Civil War would be something I'd be just as happy seeing indirectly covered as part of the exiting Imperial Conquest line, as something adjacent to the Wild West and other Victorian settings, but either way, I think the ACW would supply some great figures for geneal-purpose American soldiers for late 19th-century American conflicts besides the ACW, as well as Victorian Sci-Fi/Steampunk purposes, etc. (just add Death Fields accessories!)
Zouaves are covered by another company, but that's such a weird and diverse subject, I can't imagine that additional sets in different styles wold be unwelcome by ACW gamers. I noticed that Australian and New Zealand militias apparently used some suspiciously similar styles of uniforms to Zouaves, for what it's worth - much the same thing is probably true of other militias of the period as well. I could certainly see a Zouave kit being used along side "cowboys" against Maori wrriors for e.g. New Zealand Wars and similar gaming subjects in the age of Imperial Conquests! (For Victorian Sci-fi, it's tough to find a more outlandish and over-the-top subject for a wargaming faction than sci-fi Zouaves IN SPACE!)
And really, there doesn't seem to be a bad choice on that survey at all - choose anything at random from that menu, and I can imagine some cool army kits coming out of the line!