Hi Bryn,
I recognize your request. I general we would like the DNN core to have a provider model for payment processing. I think this is somewhere in the wishlist of a future version.
That leaves it to the module builders to come up with a solution. PayPal is rather easy to buld into a module, so this is what happened a long time ago with Events. The coding is rather straight forward.
The Events module does not have a provider or plug-in model for enhancements (yet?).
The Events team has worked in the last year to create a module that does it's work, looks resonably nice, and is stable. I think, with the upcoming 5.0.3 release we have reached that point. For the next big release of Events we are evaluating the options. If the DNN core is going to provide a payment processor provider, we will try to incorporate that in the next version of Events. If the DNN core does not provide this, I think we will wait another round for Events. Resources of the team (all volunteers) is limited and Events is a complex module with a lot of history.
So if you want to have another payment option, you could look at some commercial modules, code it for your version of Events yourself or wait. We have no better option available, sorry.