We do this all the time with kernel development, and is one reason why breaking changes up into tiny pieces is so powerful. We can take the pieces that make sense now, and allow the developer to redo the portions that are not ready yet, instead of having to reject the whole thing if it were done in one single "chunk."
Also note that the TTY/serial portions of this hardware support was already merged through the serial tree because they were independent and didn't affect anyone else.