That would require whole new sets of mechanics for the Traditions to affect.
As it is, the 8 Traditions are already easily covering all game mechanics.
Well... they
are going to add new sets of mechanics to the game. That's the Paradox model.
And when they do this, they're going to find it harder and harder to find room for those new mechanics in their existing 7 traditions.
So... good?
For the record, here's how they could play out after the diplo/espionage expansion;
Expansion
Security (renamed domination tree)
Prosperity
Harmony
Supremacy
Diplomacy
Discovery
Trade (trade functions moved from the diplomacy tree, replaced with traditions that are actually to do with diplomacy)
Intrigue (espionage focused)
Domination (has similar traditions to old-style domination, i.e. focused on being able to make better use of vassals and tributaries)
Conquest (ground combat focused)
Philosophy (focused on controlling factions and population ethics, getting bonuses from pops with ruling ethics, good for tall runs)
So that's 12 right there. I'm sure there's a couple more there somewhere, which would be 14.
Having more than seven would get rid of this thing they have to do right now where every tree has to be useful for everyone, because everyone has to take every tree if they want 7 ascension perks.