It would be great to have 9V out of the M10. My guess of why the “standard” is ~3V is because most PIP mics will “work” at low voltages and the typical use is low SPL situations such as recording voice, meetings, etc with these portable recorders. Perhaps the manufacturers assume that if you are recording high SPL sources, you’re going to be using a battery module of some sort (often wireless setups for lav mics) that puts out 9-12V. Purely a guess.
I agree. Most of the devices we use are meant for use as recorders with boundary microphones attached where a plug and play application is necessary, i.e. courtroom, board room, etc. An external microphone is an afterthought with this crowd as long as its intelligible enough. The 3v power supplied goes along the same lines - enough to get the job done with a non-professional lavalier mic.
Regarding the bold selection above:
Who is using non-professional lav mics? I wouldn't even know where to find such a thing anymore. All the lav mics I ever see are definitely "pro" quality.
How many lav mics are even out there anymore that use a 3.5mm TRS connector? Sennheiser is the only one that comes to mind, and they are using all 3 conductors for one channel.
Why continue to use a consumer-level interface and powering scheme on devices that are billed as professional units? Having a 3.5 mm stereo input is a great convenience, as a
line level input to connect with consumer-grade gear. To bill it as a "mic input" is somewhat misleading in today's context, where you'd be hard pressed to find any mics that perform properly with only 3V and also use this interface.
The only context I can think of where it still makes sense to have a 3.5 mm "mic" input on recorders such as the SD MixPre series are those little dedicated on-camera mics. I just went through all of Rode's offerings since they make a bunch, and one of them does in fact use 3V PIP. All of the others require an onboard 9V battery supply.