Is ISRU refueling really ready for this? (Methane I assume, as hydrogen sounds much harder.)

To me, getting that set of technologies to an operational level is one of the biggest reasons to go (back) to the Moon. It's cheaper to send demonstrators there, and easier to troubleshoot them.

Once we can do ISRU refueling reliably, the solar system will become dramatically more accessible (to robots, and eventually humans).

Yes, because we are sending an ISRU demo on the Mars 2020 rover which will convert the CO2 atmosphere into oxygen and carbon monoxide (which could be used as a fuel).

You'd have to use a completely different type of ISRU for the Moon, and mining for it on the Moon (i.e. scraping a permanently shadowed crater near a lunar pole) is a lot harder than on Mars where you can just suck in some of the atmosphere. There's not nearly as much commonality as you might think.

I didn't know about the ISRU test on Mars 2020, that's very exciting!

I thought the typical Martian ISRU called for heating soil to extract water vapor and using the hydrogen in that to make fuel. Oxygen is still interesting, for sure, but that robotic mining sounds a lot more difficult.

The carbon monoxide can also be used as rocket fuel. Not commonly considered, but it'd simplify a lot of things.

Zubrin's plan is specific to Mars in that it relies on chemicals present in the Martian atmosphere.

The only equivalent option I know of for the moon would be to collect water ice and break it down to oxygen and hydrogen. The process involved would be quite different.

NASA's Mars 2020 is set to collect samples and place them in a capsule for later pickup; NASA and ESA have announced collaboration on a separate sample return mission to pick up the samples left behind. Lets them save collection hardware weight on the return mission.

The Mars 2020 mission is taking core samples and caching them for a follow on sample return mission to pick up and send back to earth.

NASA has been working on it, more or less, for at least a decade. I think the latest (and IMO much less risky) proposal doesn't involve any in situ fuel creation.

Little new technology, but a substantial financial cost. One would need a much heavier Martian probe that would include return stage for the lander.