While the civic platform is used for the FR-V rumour has it that Honda won't bother with another one - if it does it'll be the conventional layout of 2,3,2 and might just be the Japanese Stream.
The civic definitely doesn't need to get any bigger, despite having not bloated as much as some cars in its class. If I was being asked by Honda for what I wanted from their next Civic (I've owned 2 Hondas, my parents own 2, my sister owns 1, my parents-in-law own 3) here's what I'd tell them.
1. Competetive pricing. You are not moving upmarket, you're just pricing out people who previously bought your cars.
2. Don't over-engine and under-engine. The current Civic has no engine that is "fine". It has an underpowered 1.4 (less so since the vtec replaced the dsi), an overpowered and unrefined 1.8 and a very expensive 2.2 diesel. People don't like underpowered cars, but a lot of people won't pay extra to get to 60mph in 8 seconds.
3. Actually employ some chassis engineers. The current civic is crap, the Jazz is only OK. The 99 Accord was actually really good, why can't Honda produce another car with a decent ride, controlled body-roll and excellent damping? Oh and MULTI-LINK. How could you not use that on the current Civic?????
4. We're not Americans. Please, please, PLEASE don't bring their dashboard and materials over to Europe. We'll pay extra, promise.
5. Road noise. Seriously, every other car manufacturer on this planet can produce a car that doesn't suffer from annoying levels of road noise. I have yet to drive a Honda car that doesn't piss me off on a bad surface and there are a lot that have annoyed me on a decent surface. It fatigues drivers, it feels cheap and it can't be needed.
6. You plan to reduce weight - good on you. Don't use marketing tricks like "carbon fibre roofs" though. Use high strength, low weight materials. Use the economies of scale to get these cheaply. Use them in your other products. If the chassis and every single component can be shaved of weight the savings will be enough to put in a smaller engine, smaller brakes, so less weight, so thinner everything else, so lower weight etc etc etc....
Have I missed anything?