That's where the buses and/or light rail systems would come into play.
A commuter line on the old CSX tracks would terminate in DT Tampa, I believe; or it could continue from just east of DT Tampa, up over the top of the bay into DT Clearwater and terminate in DT St. Pete (this route would take it through several "downtowns" in Pinellas). Right now, there isn't a plan for commuter rail in Tampa other than the proposed statewide system.
I think there are a good number of people that commute between the three metro areas (Tampa Bay, Lakeland and Orlando) that such a system is warranted. I agree with Lakelander. The CSX might be cheaper and better. In the meantime, I applaud the Orlando metro for working together to get a commuter rail line built. Hopefully, it this will put some pressure on the leaders in Tampa Bay to come together in similar fashion.