I have followed Mongolian Script Unicode support for some time, and needless to say it has had a rough road but made some great steps forward in recent years. Most recently, I have been reading through the documents
of the Mongolian Working Group Meeting #3 from April of this year. Some robust proposals (both for minimal changes and major changes) have been made for standardizing the OpenType coding and creating clear character definitions for designers and creating easy and accurate use for users (the latter perhaps most important). At the very least, we can look forward to thorough Unicode Technical Notes on designing for it, which will greatly help for interoperability among fonts.
I bring this up here both to note this hopeful step forward for Mongolians using the script and out of curiosity to hear from those more experienced about revisions made to Unicode blocks. With the sort of “set in stone” attitude Unicode seems to take toward changes to code charts (a la legacy characters), I wonder how difficult it will be to refine the Mongolian Script block even after it gets to a more unified, stable form through minor changes. The major changes would be quite a hassle to make I imagine.