Tabular unit symbols


Assuming a typeface which defaults to proportional figures, do you think it’s sane and user-friendly to adjust more characters than just digits when fixed-width, tabular `tnum` numerals get activated? I’m thinking about making currency and other symbols the same width as figures then, so they align properly.
feature tnum {
@digits = [zero one two three four five six seven eight nine];
@digits.pnum = @digits;
@digits.tnum = [zero.tnum one.tnum two.tnum three.tnum four.tnum five.tnum six.tnum seven.tnum eight.tnum nine.tnum];
sub @digits.pnum by @digits.tnum;
lookup units {
@currencysymbols = [dollar cent sterling currency yen Euro]
@unitsymbols = [percent @currencysymbols]