There is a company called the Boston Surface Railroad that has been trying to get Worcester to Providence commuter service started for several years now. They even acquired an old FL9 locomotive, which has sat on a siding along 146 for a while now. Unfortunately, it looks like they're still having a hard time getting it off the ground, though I hope they succeed.

There used to be a rail line that ran between Fitchburg and Worcester, creatively called the Fitchburg & Worcester Railroad. Currently, two sections have been converted into rail trails: the section between Fitchburg and downtown Leominster is the Twin Cities Rail Trail, the the section between Sterling center and Sterling Junction (right near the Sterling/ West Boylston line on Route 12) is the Mass Central Rail Trail. The section between Pratts Junction and Sterling Center is partially intact, but also partially built over, particularly around I-190. There are tracks in place between Leominster center and Pratts Junction, as well as between Sterling Junction and downtown Worcester. Both are currently owned by CSX. Rebuilding that rail is possible because of how the rails-to-trails laws work, but would be very expensive (see the South Coast Rail project, which is currently reactivating a long-defunct rail right-of-way). Without a greater need, I think a rail route between Fitchburg and Worcester will be a tough sell.