There are several models that still have it. When I bought my most recent phone it was one of my personal requirements. I think there were 6 or 7 models to choose from that were all essentially the same as any other modern phone, but had a 3.5 jack. That was a while ago, but there are still some new models rocking it. I use it all the time.

I am guessing the egg-shell foamed enclosure is for the sound, but you probably have a bunch of sound coming from the fan port, nessisary for ventilation. You can cut a lot of the sound but maintain the airflow by cutting an s-shaped ducting spanning the width of the enclosure. The shape will drop the sound, while then ducting keeps the air flowing. I would not recommend any sorts of filters to block the sound because they are a bit too restrictive for an enclosure in your style.

To be fair, solid state batteries went from being a pipe dream, to being only possible in perfect laboratory settings, to the current state of very real and possible -just expensive. And it has done all of this in about a decade. Just give it time.