I think it will be hard for teams to time using a pinch hitter in bottom of the ninth. They will probably want one on the expanded roster as he will be useful in other innings also.
That's kinda the point. If he's still on the bench with two outs and nobody on in the ninth, why would you send him up to hit then (almost certainly replacing a better hitter, now that pitchers won't be batting) as opposed to just waiting and putting him on second to start the tenth - assuming you get there - in which situation he is almost certainly
wayfaster than whoever he's going in for? You get the benefit you want without the guesswork of him singling and getting stranded, for example.
