From my understanding and reading, there's no requirement for FOs to have an ATP or be at ATP mins in the Senate Bill. That was just in the House Bill. The Senate removed it and instead is taking a stance that the FAA and such need to look at certification requirements and make changes there. Once that's done then they'll move on to min. hours for airlines.

Then again, I can't figure out the difference between S.915, 3371, and 1451. They all have pretty much the same content.