Ideologies should give different bonuses for diff completed policy trees.

So if you finished Commerce, your ideology should give your a bonus that you wouldn't have if you didn't finish out the policy. It only makes sense that a civ's long-held political/social ideals somehow affect their late-game ideology. It's weird for the ideologies to exist in a vacuum IMO

COMMERCE
Freedom: Great Merchant Trade Missions provide twice as much gold and CS influence.
Order: Each city generates +2 gold a turn.
Autocracy: City razing generates +15 gold a turn.

AESTHETICS
Freedom: Tourism output raised by 10% in the capital.
Order: Great Improvements yield +1 culture.
Autocracy: Plundered Great Works are twice as effective.

PATRONAGE
Freedom: Each allied CS raises total Tourism output by 2%
Order: +2 happiness for each allied CS
Autocracy: Allied CSs get a 50% bonus to unit production (and militaristic ones make units for you twice as frequently)

Stuff like that, what do you guys/gals think?

Just thought I'd add: if the 3 ideologies gave different passive bonuses for the completed policy trees, switching ideologies won't be as scary a proposition as it seems to be now. Rather than losing all of your bonuses, you'll still have the bonuses for completed policy trees, albeit differently focused.

PIETY
Freedom: Cities generate +1 culture for each religion found in it.
Order: Cities with majority of your religion generate +3 culture.
Autocracy: Occupied cities of a foreign religion generate half the unhappiness.

Reports put the number of tenets for each Ideology between 12-16, so it would seem for there to be a lot to choose from depending on which victory type you're going for. Doesn't seem like there's a need for automatic bonuses.

Yeah, given that you can get up to 14 ideology bonuses, I don't need different finisher bonuses for the other trees.

When you want to add something, you should always ask yourself "what does it add to the gameplay"? If it just adds stuff (and is as your suggestion posing balance problems) without changing anything, you need to ask yourself if it's really worth it.

Your proposal wouldn't change the way I play at all, I probably wouldn't even take notice of it. Which late game ideology I chose will probably be more dependent on the tenets in it as well as what the other civs chose.

I think that that would be very useless. There are enough tenets that we don't need ones catered to which track we choose earlier.