About half of the repeaters that I've come across do transmit tone squelch which makes monitoring and scanning that much more pleasant.
Amen.
I've only come across three repeaters in my area so far that use DCS.
I (co-)run one that uses DCS. It's the only one I know of :)
I don't know any of the current "ham" radios that support different DCS codes on the input and output (the same goes for tones), nor do I know of any of them that allow you to send DCS without requiring it on receive. In other words, you can transmit a tone without needing it on receive, but you cannot only transmit a DCS code.
I recognize that this limits chirp's applicability to a very few niche ham repeaters and/or potentially some commercial repeaters. I'm certainly not saying that CHIRP *shouldn't* support such operation, but I don't think the audience is wide enough to justify me spending time on it instead of something else. If I'm wrong here, please speak up.