This one surely has to fall in the class of problems that have low returns/economic impact and yet tend to occupy the public sphere of debate. However:
1. It is entirely sensible from a pure economic theory point of view - the same constrained resource (footpath) is being demanded by two sets of agents - one is the dawdling shopper and the second is the busy worker bee. Since the demand from the resource is different (the former wants to have a good-time window-shopping and/or shopping; the latter wants to cover the distance as rapidly as possible), it is only sensible that a solution to this problem be attempted.
2. While dividing the footpath into fast/slow lanes sounds sensible, there is an obvious issue of enforcement. It is a bit like designating a minimum speed by lane on a highway and penalizing anyone who violates this rule. It is close to impossible to implement.
Finally, two things stand out:
1. Similar rules have had some success on roads for vehicles (differential tolls by lane/dedicated car-pool lanes etc) - however, given the whole sensitivities involved in a plebeian activity like walking, the hackles are up immediately when there is any mention of 'segregating' pedestrians. Although the underlying economic logic is exactly the same in both scenarios.
2. One continues to marvel at the dogged attempts by the state machinery to put in regulations that are pretty much un-enforceable !