From technical point of view, the program like TuneText could be developed at least several years ago. Why nobody did it?

1. We cannot integrate text editor into HTML code because the resulting page will be too big.
Yes, we can! Size of HTML pages is not increasing:
They contain just reference to TuneText editor, which is spread between separate JavaScript files. Its overall size is under 100K, and that is shared by all pages.

2. Resulting HTML pages will work too slowly.
There might be a small delay only during loading the first page. But after that, a copy of editor will be available for the rest of pages in the fast cache.

3. We should always use a full-featured text editor, like Word.
Well, face it: In the most cases we don't use and don't need all the features!
TuneText provides users with a reasonable compromise, - a carefully selected set of features that are used most frequently.

4. The userData space is too low (as little as 64K).
First of all, we are talking about size of changes, not HTML or text flow. Thus, even that minimal 64K becomes quite impressive multi-pages' volume of data.
Nevertheless, it can be a point. Obviously, TuneText is unable to support, say, one million changes. However, any customizing aims to help only one person at a time. TuneText is a tool for "one reader" (or user's account).
And average reader NEVER makes 1 mln. changes!!!

5. Why TuneText works with InternetExplorer browser only?
It's your choice, - about 90% of Web users worldwide use InternetExplorer.
If required, future versions of TuneText may be updated to work on all browsers.
In fact, the very first TuneText was a cross-browser code!
However, this requires a serious compromise in terms of speed and size.
The current TuneText is perfectly optimized for InternetExplorer!

But once again, this depends on your demand!