I have written about this several times (most recently in this thread) and I would definitely buy an Apple e-ink device. It’s extremely frustrating not to be able to use one within our personal Apple ecosystems and whilst it would definitely be a smaller market than their other products, it’s no different to them producing the Vision Pro, which will also be a small market. I’ve been extremely frustrated by my experience of having to go elsewhere to find the device that I need.
For what it’s worth though, I went with Boox which is Android, which I felt under the circumstances was the closest I could get to what I want. Which is basically just an iPad with an e-ink screen.
Someone mentioned the Daylight Computer in this thread, which aside from lots of marketing blurb doesn’t seem to be doing anything novel. The Boox Go is already at 300dpi. The experience on an e-ink device would be slower than on other iOS, there’s no avoiding that, but otherwise such a device would be fine. If Android software is fine I have no doubts about Apple’s abilities to accommodate it.