I could see Richmond working as a point to point airport ( those not wanting onward connections) for Western Sydney , along similar lines as AVV is to Melbourne, but with increased frequencies & destinations. Western Sydney has a population of around 1.5-2 million which is expected to be close to 3 million over the next 20 years , with a lot of this growth being in the NW part of Sydney where Richmond is located. There a numerous large business & industrial areas in western/ north west sydney that would love the choice of not having to endure , in some cases, 2 hours drive from SYD . It would also provide quicker access to the Blue Mountains for both residents and visitors.
I could see Richmond supporting services to most capital cities & high profile leisure destinations(i.e. OOL /CNS) in varying frequencies. In addition , opening it up to International (not restricted too , but mainly LCC ) as being an alternative to SYD. Agree , a substantial investment in infrastructure support would be required to make Richmond a viable alternative.