If you can /speak/ over a phone connection, you can send a fax over a phone connection.
I was thinking that, modem too, but I also recall there's clever processing in audio-to-digital encoders which can filter stuff out to enhance voice audio.
I presume the current rules are 'fine, you can do that, but it must not bugger up fax tones' and the proposed change will remove that requirement. It doesn't necessarily mean fax won't work, but there will be no guarantee that it will work, no requirement for it to work.