A new type of map view overlay is not possible to implement as far as I know. Hover text on individual tiles would be a disaster as a gameplay mechanic, since you would have no way of evaluating the best overall path to take, and with each movement point on each turn you'd be forced to stop and look at 3 different tiles, at least, to see which is best. It'd be tedious and annoying. Also, programming the AI to pathfind through such a maze would be pretty easy, but it would add a lot of computation time to the turnovers which can already get pretty slow, for an unnecessary "fluff" type system. Ceph, there are those of us who would be enormously grateful should an update of this sort for the Civ4 version be forthcoming in the future... Hopefully we can reverse-engineer it from your Civ5 version though if we have to, heh.