I think there is a middle ground. Apps could announce the upcoming railroad crossing just like they do with a left/right turn. Somewhat of a silly example, but if there is a river at the end of a road and your only option is a left or a right, the app will not help stop you for driving the car into the river, but the instruction to go right or left does (albeit accidentally) help you avoid that. I don't see why it won't do the same with rail crossings.

Although you should focus on road signs more than you do the app, there could be a dangerous situation in which the app says "make a left turn at the light", but before reaching the light there is a railroad crossing. Of course you need to stop at that, but the app can enhance the situation but treating it like another instruction. I see no problem here but an overall safety enhancement.