Since the upcoming parandur airport gonna be build way outside of the city limit,so building new metro to airport is bit pointless.
But,it'll help the kelambakkam commuters to be connected with existing cmrl network like connectivity point.
What you are referring is natural grass(native to india) which is typically dark green. Our cattles love to graze them as they are plentiful in rural areas.which is naturally occurring.
The grass we mentioned here are called ornamental/decorative grass which is typically grown in nurseries and...
Apart from the reasons you mentioned, we need to use enormous amount of agua to keep the buggers alive,also we need man power to trim them.
I would suggest planting native trees along with rain water harvesting setups to be more l functional.