There is!

GM Grejuva

>>Speaking of the Venn diagram, isn't it mislabeled? High Sorcery is labeled as 3-way mixes but all High Sorcery spells are dual mana frequency mixes that involve the confound.

Consider those spell descriptions as referring to the dominant foreign ingredient. Using completely made-up numbers, Saesordian Compass -- described as a Holy-heavy blend -- might be composed of 90% Lunar, 9% Holy, and 1% Elemental.

Each high sorcery spell involves three types of mana to one degree or another. This is a slight clash between M2 and M3 lore, and we haven't always done a good job of portraying this, but it has been the case since the birth of M3.

Mechanically, only the second type impacts the casting calculations of high sorcery. With low sorcery, mana types don't impact casting calcs at all because their mixtures are even more imprecise.

GM Grejuva

PS: None of the sorcery mechanics I talk about here applies to guilded Necromancer books.

>>In general, would developments in this direction be along the lines of "Low Sorcery has always existed, now it's just available for players" or "The Realms are experiencing a concerning rise in Sorcerous activities."

Mostly the former, with a dash of the latter. Players had access to Low Sorcery spells in the past -- Energy Manacles, Limb Disruption, Mana Disruption -- which just were under differently named spellbooks. The two Low Sorcery and Lay Necromancy spells tentatively closest to release (not the aforementioned ones) are going to reemerge from the dark pages of Elanthian history, rather than being modern inventions.

GM Grejuva