Hedge Magic and Mythic Blood

Hi, reviewing the old and wonderfull Hedge Magic revised Edition, and having near the Rival Magic, there are one special reason to forbide Mythic Blood to all the magic Schools with the possibility to use magical Focus? Or can we apply the rules of the Rival Magic and leaf take that Virtue on some extent to Hedgies (with the exception of the Vitkar)?
I can imagine that partially the Mythic Blood can be taken with separated Virtues, but on the schools with permission to take Magical Focus i can imagine easy ways to be descendant of magical beings or wizards very powerfull... Grruagrachan specially (and similar schools) and the same with the Witches with the Rival Magic rules about no Art oriented Traditions.
Some thought?

Hedge Magic states on p.11 that only Gifted characters may take Hermetic Virtues and Flaws.
It also lists explicitly which Hermetic Virtues and Flaws are available to each tradition.
Viktir are the only tradition that gets Mythic Blood.