I wonder what would happen if Australian public transport went to an open gate system very similar to many parts of Europe.
In such systems, there are hardly any fare gates (if at all). It is your responsibility to obtain a ticket before boarding transport. In many cases, you buy the ticket from a ticket machine and then you validate it by putting it in a separate machine, usually close to the bus stop / train platform (this stamps the generic ticket with the date and time, so you can't just reuse the same generic ticket). Naturally, there are seasonal tickets for those who use the system more often than tourists who would use the system sparingly.
There are stiff fines (well, relatively stiff anyway, e.g. EUR 80) for being caught taking transport without a valid ticket (i.e. without a ticket at all, or with a ticket which hasn't been stamped by the validating machine).
Overall the system relies quite a lot on honesty (it is possible to "ride the transport system for free" as long as you can evade being caught without a valid ticket), but IMO it also results in a relatively quicker system for boarding as less time is spent on boarding for people to validate their ride - instead, here they just simply hop on. Probably a minimal effect for trains (as trains you traditionally need to buy a ticket in advance anyway - the major advantage would be no ticket barriers required at stations, so improved traffic flow) compared to a greater effect on buses. I can see that a lot of people right now would say that it makes fare evasion (particularly by students) far too easy..... so I wonder how the jurisdictions that have such a system deal with such an issue.