I have been wanting this since I first used whisper and saw it’s capability. Nothing you can buy off the shelf is sufficient at the moment and if you diy it’ll be too big.
I actually pitched this idea as a project for students on an MSc EE course a friend runs. Sadly none of the students picked it but we looked at it in some detail and it’s so simple that even the dev boards +battery + mic array could have been made pretty small (according to him anyway). I really hope someone with the hardware chops fancies scratching the itch!