If we went metric on the interstates, exit 880 on Interstate 10 in Texas (at the Louisiana state line) would retain it's status as the highest numbered exit in North America. Only it'd be exit 1408.
(exits are generally numbered by their mile (err, kilometer..) marker in the US, not consecutively)
Not really true. In New England and most of the NE, exits are numbered consecutively, or at least started that way until ABCs got added in and others got removed.
So switching to metric would give the various DOTs in those states the opportunity to correct their numbering. They'd have fewer A,B,C exits as well, since kilometers are smaller and would increase the chance of the exit location falling nearer to a milepost.
(exits are generally numbered by their mile (err, kilometer..) marker in the US, not consecutively)