i have a dream to build the perfect dual-purpose convertible bike..

maybe start with a slightly old school track frame with angles not too steep...
it would have upside down riser bars or mustache bars in a major taylor type adjustable stem..
when you are feeling agressive stretch the stem out a little and get the bars low,
when you are cruising, flip the clamp over and back it up a little and you have instant upright position with lots of rise, no need to remove the bars or even the clamp....

then if you ReallY want to cruise, throw in a different rear wheel built up with a 2speed bendix kickback hub..
no cables, no brake levers... still lots of versatility