As for custom IEMs: I'd definitely get me a pair when a truly wireless option from a known player in this space (Campfire Audio, JV Harvey, UE, etc) that sounds great and has a great mic comes on the scene.
I tried Bragi's offering years ago. (Bragi was the first manufacturer to try at truly wireless headphones. They released before Apple launched the AirPods. The AirPods are now a billion-dollar business, whereas Bragi is defunct.) They partnered with Starkey, a very popular hearing aids manufacturer, to make the (still only) waterproof custom true wireless earbuds. The idea of using earbuds that fit me perfectly that I could shower with was awesome. My right ear canal has a weird kink that makes it difficult to use regular IEMs and impossible to use the truly wireless options at the time, thus making the Bragi's even more lucrative. They also partnered with Mimi Audio to offer an EQ that was tuned to your hearing...on iOS. Impossible to beat feature set.
Unfortunately, the earbuds were a disaster. Worst $600 I ever spent. ($600 is cheap in the world of custom IEMs; another reason why I got them.) They didn't sound very good, the audio balance would shift right after an hour of listening, the mic was AWFUL (i made many, many excuses for it, but it was just plain bad), and, worst of all, because the base of the earbud was large (stuffed with ICs) and Bragi chose to use the same case that they used for their universal offering, the nozzle didn't go deep enough to provide a truly locked-in seal. This is, like, THE reason to get custom IEMs, so them failing here was especially painful. The local audiologist (you had to go to a Starkey "dealer" to get your impressions) got tired of me coming in for refits, and I got tired of waiting three weeks to have earbuds I'd use for three days.
I was done with them when Samsung released Galaxy Buds that were compatible with iOS and had noise cancelling. Threw them in the trash. The case even had my name on it. One of the few things I ever engraved with my actual name...and I threw them out because they frustrated me so much.
ADV-Sound has an offering here, but apparently their mic is not very good, and info on these headphones is lacking, Sounds very Bragi 2.0-ish to me, so I'm passing on those.