There are no bandwidth issues. And for those wondering about the difficulty, if you think about it for 1/2 a minute, the facility already exists as Joe and the clones have it. It may need a bit of tuning to prevent unuthorised HTML for example but largely it would only be a matter of extending the use to others.

Whether such a change would be desirable or not is another matter. Most systems I use allow editing and don't have problems with abuse like re-writing history. In the case of Mudcat, it is rather tempting to suggest it would be useful above the line but likely to be a liability below the line...