The Rangers not only can trade him but will absolutely get pieces of value in return for him, without retention imo. The NHL holds Trouba in a much higher regard than our fanbase or the analytics community. Detroit, Florida like you mentioned, but also could see teams like Tampa, Nashville, even the Canes getting involved to fill their leadership void. I assume Trouba will block the Canadian teams and bottom feeders, but that leaves a lot of suitors.
This all being said, the odds of him actually getting traded are pretty low. He also has only 2 years left and is a prime candidate for LTIR f***ery the next 2 seasons with the nagging injuries piling up. It's not like he is dragging the team down to the basement. Plus he is well liked by his teammates, which matters.