One critical point needs to be addressed, otherwise these kind of changes to magic are a serious settings regression. Since master quests are blocked out (settings wise circles not promoting masters of opposite circles etc.), how new players are supposed to get glyphs which come from the master quests? According to the settings glyphs are occurring in the nature and can be obtained from the glyph hunters. I.e. according to the settings there is no direct logical relation between being a master in some way, and obtaining glyphs. I.e. someone who for example avoids circles, can still be trained in magic up to high levels and getting the glyphs can practice spells. But if the only source of glyphs are master quests - it creates a problem.
Secondly, since circles become now more closed, you need to provide some "out or circle" trainers. Magic is a phenomenon not bound to social groups (which circles are), so if some powerful mage doesn't belong to a circle, he/she still can teach others. Introducing such kind of societies will broaden the settings. But the most serious issue is the first one. If it won't be addressed - the current magic system can be considered crippled.