Well that was just his way to say, what is happening with my lovely milk bottle teat?? Hehe. This is just a precursor as to how he would be at three to things he doesnt want. (sorry i just realise that i was reacting the same way to ds when he was younger but i am now paying for it LOL wish i was a bit more forward thinking). Back to the issue here. If you want to cut down on the milk, i would say, go for the sippy. Do as you mean to go. We didnt but DS is a hungry baby and without a full tummy, we would get numerous NWs and EW, so for our sanity and sleep, we chose to leave it and he was still on it until 35 mo. He gave up one evening and didnt want milk anymore.
There is no problem with his teeth, from using the teat. So weigh up the goal and pros and cons and see what you would like to go for. When he has a tantrum, just tell him that i know you dont like this one as this isnt the same as the old one. Do try it, u will grow on it one day and just keep talking to him calmly, you will be surprised how he just calms down, i hope!

. Now i am reminescing how DS was still drinking from a broken teat so carefully not to leak everywhere because i told him i wouldnt buy a new baby thing again.
oh and since you are expecting, perhaps get him to wrap them up with you to save it for the baby

. HTH xx