Truly wild timing — @alexanderjulmer and I have been working on this exact problem for the past few weeks. We just published @handlewithcare/prosemirror-suggest-changes - npm, (GitHub - handlewithcarecollective/prosemirror-suggest-changes)!
It looks like we took a very similar approach! We opted for a “decorator” around dispatchTransaction, rather than appendTransactions, and made step handlers for the other step types as well.
If you’re interested in joining forces, I’d love to collaborate!