Simulcasting on FM is an excellent move. Now, when you are in your car flipping channels, you dont have to find that damn AM/FM band button. That's a big deal for many people.
Being on FM will immediately slightly lower the demographic -- maybe from 70 to 65, but it still lowers it. Plus they now have the potential to attract younger listeners. They could not do that before when they were only on AM. They will always be the big mother heritage news station, but i would watch for some tweaks after this. They will be slight each time, but very calculated.
Notice that most of Cox's AM/FM news/talk simulcasts are the main AM signal that covers the market well and an FM move-in that's not quite as good.
Curious, did they turn off the stereo pilot? Years ago, some FM recievers were built with a selector switch of AM/FM/FM Stereo and when you had the knob in the Stereo mode, it would not pick up mono stations. Most FM talkers back then (and there were a few) kept the stereo pilot on for that reason. But now, there is no point. Plus, the mono signal will travel further.
They might change the call letters, but they wont move the WSB-FM letters to 95.5. They will find something 'similar' like WWSB, WSBB, WSBF, etc.