I'm guessing that you will still use UTF-8 for the majority
of the text except for instances in which unicode does not
specify a proper glyph (ex. the "peace be upon him" in Arabic
glyph), etc.
Who said so? "Peace be upon him" is encoded in unicode but it's not part of the Quran text but Sunnah or Hadith!!. Most of the Quran symbols are already encoded. Can't you read this? ﷺﷱﷰ