To take this to another level of nitpicking, the unit is actually kelvin. Always lowercase for the name, uppercase for the letter, whenever the unit is named after a person. Hence watts (W), amperes (A), kelvins (K), but liters (l) and meters (m).I'd like to point out the unit is called "Kelvin", not "degree Kelvin". So it's written 273K, not 273°K, and pronounced "273 Kelvin"


As for the "compelling reason for going metric", it would probably involve the meter itself: units of dimension would be in need of international matching because hardware built to specific dimensions needs to be matched exactly. Temperature and liquid volume are more "by-the-bucket" things, and derived units such as force or electric potential would involve enough math to accommodate a conversion or two, but standardizing on a certain size of screw is straightforward enough, with obvious benefits.
(For the obligatory anecdote, one poor pilot was blown out of his cockpit but fortunately got stuck in the frame when the windshield separated due to incorrect screw size. The article at http://en.wikipedia.org/wiki/British_Airways_Flight_5390 doesn't mention the metric-vs-imperial issue, but it applied to one of the screw types involved. Inability to acceptably buy or sell hardware abroad is a serious handicap where unique domestic standards of liquid volume measuring generally are not.)
Timo Saloniemi