Hi coolman,
Great domain and as spacey says " so many possibilities" Would be worth developing, but where do you start.
Sub-domains would be great as well, if you want to sell PM me a price, otherwise keep to develop.
I highly doubt this would work as should the lessee not also have the equivalent domain minus the . then they would loose far too much traffic.
For example should a car trader lease 'cars.online.com.au' advertise it everywhere, how often do you think people are going to accidentally type in carsonline.com.au instead?
I see the only true potential for this domain as a portal for online services, therefore using the suggested sub domains for categories.