You should get into contact with
PeterT as he's also volunteered to help with maintaining the Kobo the driver but is also trying to reverse engineer what
davidfor did.
From my (limited) understanding from looking at the code (and I'm sure people will correct me if I'm wrong; please do!), when new devices enter the market, entries for its Product ID needs to be entered into the driver so Calibre can recognize it. This can be gotten from looking at the firmware, but if you want Calibre to support it on Day 1 release, that'll only work if you get access to pre-release firmware (ex. You're a Kobo Beta Tester), or if you ask Kobo really, really nicely.
Next, each device has a minimum firmware version, which I think is the version it ships with (because it may be a device specific version not released to the public) which you'd need to input. This is so the device can work out of the box with Calibre, even if there is no upgrade available at time of release.
In terms of database schema changes in between firmware releases, the driver would need to be changed to deal with them, and the database version number would need to be incremented. To figure out what changed, you'd need to look at the database that gets shipped with (or upgraded by) that firmware version. I think davidfor was able to keep on top of that because being a beta tester, he had access to pre-release firmware and could peek at the accompanying database files to see if anything changed (of course, in order to keep confidentiality, he'd only commit code changes after a new device or firmware was officially released, which is why Calibre support sometimes lags behind by a few days).
Finally, the Max Firmware value would be updated once new firmware was released and verified that everything was still working (was more important in the beginning when database schema changes were more frequent; less important today as the db rarely changes which is why it's (usually) safe to check the Unsupported Firmware option while waiting for Calibre to catch up).
That's about all I could glean by looking at the
driver code and the
commit history to see what davidfor did whenever new firmware or devices came out. But while I'm a computer scientist by degree, I'm not a strong coder so I'll leave this stuff to people who better know what they're doing, with my sincere gratitude and appreciation that they're picking up the mantle.