It also sits about 5 miles from Iceland's only international airport, so could prove especially disruptive to the entire nation.
That's not strictly the case. For example, Akureyri has some international flights: https://en.wikipedia.org/wiki/Akureyri_Airport
Keflavík is obviously the only major international airport in Iceland though.
A while back I remember hearing a proposal about expanding the airport in Egilsstaðir to be capable of replacing Keflavík if (when?) it is disrupted by lava flow. I think it proved too expensive for much action to be taken though. It would be interesting logistically to see what would happen if Keflavík was knocked out of service.
I actually see Tampa International this way. Its literally on the coast, and just barely missed near two near Cat-5 hurricanes in two years. And that risk is not shrinking.
Lava flows came very close to Goma airport
It looks like Kilauea lava flows in the 1880s came within a mile or two of the site of Hilo International Airport. Lava flows earlier this year were heading in that direction.
It also appears as though the airport was hit by tsunamis in the 1950s and 1960s.
Iceland beginning, let alone completing, a major infrastructure project in the 21st century? Impossible.