>>8051426Nah. B2Five claims modularity but it's pretty simplistic to be honest. It's a fine toyline but I wouldn't say it has great customizability. And Rihio are model kits.
>>8050224I think your best bet is probably Diaclone or RobotBuild. Diaclone has decent buildability/swappability, and I'm not sure how deep RobotBuild gets yet (since none of us have it in-hand yet) but it seems to have basic Diaclone compatibility. Diaclone is really pricey though.
Assemble Borg is also a choice. I'd say a lot of it is more organic-looking than most of these other robot lines, but it offers great buildability. Like Diaclone, this is going to be a pretty expensive line to get into.
To be real, my best suggestion would be Hexa Gear, but those are kits too. If you're willing to put up with building, Hexa Gear gives you a ludicrous amount of customizability and it's also compatible with Koto's Frame Arms, MSG Weapons, etc. kits, so you have a shitload of parts to choose from. Look at this beast built from various Hexa Gear and MSG parts. You can get truly inventive with this system.