The question in regards to bluetooth speakers were asked almost every single year I have been involved with VEX, so it is very unlikely to be legal this year, especially since the common sense of R12 part b. does not include any speaker other than the VEX ones implying that any non-VEX speaker is illegal:
If using the VEX speaker (276-1504), the chosen audio must not be distracting and must be in
good taste. The Head Inspector and Head Referee will make the final decision on the appropriateness of the audio
BUT, if you are in VEXU, there has been ruling two seasons ago that state non-VEX speakers can be used as a legal non-VEX sensor if they are used in a manner to provide some sort of input:
To simplify things, if you are in VEXU you can use a non-VEX speaker as long as it’s used as a sensor, but if you are in VEX EDR it is not legal to use a non-VEX speaker in any way, shape, or form.