If it was dependable and could do the run in a reasonable amount of time, it would probably be worth doing. But you would need to put in more double track. There is quite a bit of freight traffic on there right now.
I would expect some interest from Lakeland, Plant City, etc., to Tampa for commuters, and possibly even from JAX and ORL, and perhaps the other way as well. Right now, Amtrak in it's infinite wisdom, has made it literally impossible to commute from Lakeland to Tampa, even though you could theoretically have done it with 91/92. When they truncated 89/90, Palmetto, to WAS-SAV, there was no longer rail service to Lakeland and Tampa. They realized that was a major goof, since Tampa sees quite a lot of passenger traffic, and they had just cut them off from passenger rail service. So they added the current dog-leg on to 91/92, to service Tampa and Lakeland. When they started that service, it was originally scheduled so that 91 got to Tampa fairly early in the morning, and 92 picked up in very late afternoon, so that someone from the Orlando corridor, or someone at Lakeland, could have taken 91 into Tampa , worked all day there, and then commuted back on 92. That actually would have worked for anyone in the Orlando corridor that \wanted to do a day trip to Tampa. Even folks in Jacksonville, theoretically, could have made day trips to Tampa and gotten back the same day. They would have had to get rolling awfully early in the morning, but it would have been do-able. We even took that run once (fromWPK), and spent an enjoyable day in Tampa.
But Amtrak shot themselves in the foot two ways on this one. First, and this is still the case, you CANNOT travel between Lakeland and Tampa on 91 or 92. Amtrak won't allow it. You can't buy a ticket to go from Lakeland to Tampa, nor can you purchase a ticket to ride from Tampa to Lakeland. So a potential commuter from Lakeland to Tampa and back is prohibited from riding. That's plain stupid, IMO.
Second, they then changed the schedule again, so that there are only a couple of hours between the arrival of 91 and the arrival of 92, at Tampa. If 91 is running particularly late, you can't make the connection at all, and would have to do it at Lakeland.
I don't know if the passenger traffic exists, or could be developed, to make it feasible, but if 91/92's schedules could be rearranged to again provide a fairly reliable day trip and commute capability from the Jax-Orlando-Lakeland corridor over to Tampa and back, they could add a car onto the end of 91 at Jax, cut it at the station at Tampa, pick it up and add it at Tampa onto the end of 92, and drop it at Jax from 92. At Tampa, 91 and 92 both back into the station, so if they wanted to do this, it would be fairly easy to just drop that last car at Tampa and pick up the last car at Tampa. They'd have to do some switching at Jax, but they used to do that with the Express boxcars, and I think they still have an engine available at JAX to do switching with, and they have storage tracks at both locations. JAX is a crew change location for 91 and 92, so the arriving engineer ought to have plenty of "hours-of-service" time left when he/she arrives on 92 to do the switching, with the new engineer taking over 92 available to continue on north with 92. I don't know how close the southbound 91 engineer usually is to his hours limit, but one way or the other they ought to have the people available to do this. On 97/98, those trains go all the way from Miami to Jax with one crew, so there ought to be more than enough slack left time-wise for the Tamp-Jax and Jax-Tampa crews to do a little one-car switching if necessary. If the extra coach needed service, they could simply leave it on 91 instead of dropping it at TPA, and take it down to MIA for service, and put a different one on to that morning's 91, pick up the commuters and so forth at TPA, and drop it at JAX that evening.