I'm really interested in this project: a request from a particular industry to provide a valuable, bespoke product. I'm ready and willing to work on something like that.

But the above questions are important.

"Track Changes" is included with Microsoft Office (so we compete with free). Printing on paper is also free.

A worse problem: the article is not clear enough about what editors would actually value.

Dear Karina Palmitesta: Commission someone to build exactly what you want, get your staff to test it and provide relevant feedback. You should expect to pay for this. If you believe you can sell this to your peers, negotiate a profit-sharing agreement. You should still expect to pay for this.

The existing (annoying) tools she mentioned seem to be simply Word and printing things out on paper.