@Dave: Please note the changes in the default style. It would be great if you could test this patch and maybe suggest a better description of the two options.
Sorry for the delay in responding. The modified r3598 produced output from the echotags function. I did not see anything regarding the exit_to tags but my test destination tag was processed and this output went to stderr:
4611686018427392234 (168231839) - [highway=motorway_link,destination=Beltline Road East,mkgmap:exit_hint=true,mkgmap:dest_hint=true,bicycle=yes,mkgmap:way-has-pois=true,mkgmap:exit_hint_ref=195A,mkgmap:label:1=Dest: Beltline Road East,oneway=yes] before
4611686018427392234 (168231839) - [highway=motorway_link,destination=Beltline Road East,mkgmap:exit_hint=true,mkgmap:dest_hint=true,bicycle=yes,mkgmap:way-has-pois=true,mkgmap:exit_hint_ref=195A,mkgmap:label:1=Dest: Beltline Road East,oneway=yes] after