Mass availability of microphone, earphone and DSP technology should make hearing aids cheap. I suspect that the technology isn't quite as trivial as the article suggests, hence the patent moat is effective. Probably it's the speech intelligibility tweaks that are specific to the incumbents, and not of much interest to the wider tech industry. Some open source DSP algorithms based on what ever published research is out there could be a good start.
This blog is such a mess to read. There is a little bit of somewhat useful info about the hearing aid industry, but it’s padded out with a whole lot of unrelated junk.