Opal has been promised as the solution to Sydney's fare mediocrity. It is not at all clear that this is correct. What is entirely possible is that MyZone fare structure will be sold through Opal. MyZone is not an integrated fare structure, it is a differential fare structure. Integrated fares would require a mode blind single flag fall system. IPART (Independent Pricing and Regulatory Tribunal) have been quite vocal against an integrated fare system. Politicians don't like changing it much either as it leads to either some people suddenly having to pay more, or significantly less fare revenue.
What Opal will surely be is an integrated ticket, which means a single ticket which can be used on any transport mode i.e. Cityrail/STA bus/private bus/ferry. This should free users from the need to purchase separate tickets for each mode constantly. It is not clear whether it will free users from loading certain passes on to the card to obtain the appropriate fare, as applies with Melbourne's myki.
An integrated fare system is the first step in a transformation in Sydney's public transport. If you are coming from Bondi Beach to the city, you should not need to pay extra to get off the bus at Bondi Junction and get on a train. Ceasing to discourage these types of transfers would be very beneficial for the efficiency of the system overall. The train costs the same regardless of how many people use it and has no capacity issues, however if more people use the bus then more buses must be run. Within STA there are a number of routes and deviations on routes which only exist to remove the need to transfer.
It is possible that, like Brisbane, an integrated fare system would be implemented and the needed restructures to bus routes not occur. There would still be some benefits in this case. At least people can escape the George St traffic jam by getting off their morning bus at Newtown and using a train, for example. These created spaces on the bus can also then be reused on the way to the CBD.
Every other major Australian city has already implemented an integrated fare system, including Canberra. Adelaide did it in the 1960s. Auckland is planning to implement it this/next year, and Wellington will likely follow. Christchurch already has a one free transfer system.
I fear that Sydney is going to be left as the only city in the region without an integrated fare system.