It would be nice to see this actually happen, but I'm very cynical that it ever will.
The big greenhouse, might be nice in itself, but won't change the town much without all the other things happening also, which seem a much taller order.
How do they intend to bring the Wandle back to the surface? Surely that would involve demolishing a vast number of buildings and things that have been built on top of it? And similarly for all the parkland.
I like the idea of taking Wellesley Road down from 8 lanes to 2. Perhaps the resulting traffic problems will encourage more people to take public transport rather than driving through Croydon. However, I suspect that it will just mean that citizens will complain and it won't happen.
If it does happen, I imagine it will end up being something looking about as natural as South Norwood Lakes (currently the largest open expanse of water in Croydon, which is a shame as it's not very big), which looks strangely like an oversized swimming pool with ducks on.
Nice idea, which I'd love to see actually happen, but the skeptic in me says it probably won't. Maybe Croydon could being a cleaner greener place to live by starting with smaller things first. Actually collecting recycling from flats as well as houses would be a good start.