One major drawback is lack of support/engagement from hardware vendors. They pretty much assume you are using C, and all of their IDEs/SDKs/codegen tools/whatever are written with that assumption. This probably isn't going to change any time soon (ever?).

My assumption is that with the advent of rust getting into gcc, you will see at least some of these changes starting to make their way into toolchains. Probably not for the MSP430, but possibly for the next generation of embedded chips.