I think they're saying that we can hope that three shots gives long term resistance, as it happens for other vaccines. We can only hope, and it's not a totally unrealistic hope given how other vaccines work.

What are these other vaccines? are the vaccinations for other coronaviruses? I'm not a biologist so I'm not seeing the connection. Is there reason to believe adding more doses would make the prevention jump from less than a year to a decade?

You can see the recommended vaccine schedule here. Several include 3+ doses.

https://www.cdc.gov/vaccines/schedules/hcp/imz/child-adolesc...

I'm aware of the 3 dose vaccines - what I'm asking is if there's any connection between the duration and the type of vaccine and the type of underlying virus.

The flu, for example as existed longer than COVID and we do not have a "3 dose" vaccine that prevents the flu for a decade. Why would we expect this for COVID as opposed to an annual booster?

HPV is a 3-dose vaccination in most cases. I believe Hep A and Hep B vaccines also have 3-dose versions, but I'm not sure if the 2 or 3 dose schedule is standard.

We don't know how the protections in the current vaccines are going to play out until we investigate them more.

Agreed, but we already know how 2-dose plays out with respect to Delta. The article in question is investigating how a 3rd dose fares against delta. There are also delta-specific boosters coming out soon.