Local loop unbundling only made sense for traditional DSL since there is typically a dedicated pair of wires back to the CO that some other company can tap into and truly provide better service. With Time Warner Cable, or even AT&T VDSL (U-verse FTTN), there's a lot of shared infrastructure between your home and the central office. That makes the prospect of "unbundling" the infrastructure from the provider less technically feasible.
In both cases there are already choices of ISPs: Earthlink Cable, and DSLExtreme TrueStream. The choice, however, is mostly an illusion. If the connectivity sucks, "having a choice of ISPs" doesn't really do you a damn bit of good, you're actually renting the same connectivity you would have had from the incumbent provider. Speeds and pricing (the things you really want competition for) are also pretty much dictated by the incumbent. About the only thing it's good for is the possibility of improved customer service or add-on services like email servers. With the incumbent taking the lion's share of the profit, those improvements tend not to be so great anyway.
With old telephone infrastructure not able to keep pace with old cable infrastructure, we're facing a true monopoly. We need to encourage deployment of new fiber infrastructure or other alternatives. I'm afraid making existing companies share their aging infrastructure isn't going to be very fruitful.