My problem with Assasinate is it's not really viable to be multiclassed ASSASSIN. A Ninja Assassin for example is totally non-viable you can't have Monk levels without massively impacting your assassinate DC.

I would like to see Assassinate changed thusly:

DC X + 1/2 Rogue Levels

Right now ignoring capstone bonuses a 19 rogue loses 1 DC to a 20 Rogue, and a 14 Rogue 6 somethingelse loses 6 DC (which results in a basically non viable flavor build ESPECIALLY after the Capstone is improved)

After this + 1/2 Rogue Levels (still ignoring capstones) a 18 rogue loses 1 DC to a 20 rogue, instead of losing 2, and a 14 Rogue 6 something else is only losing 3 DC's instead of 6.

Or you could put a version of assassinate into the Ninja Spy tree maybe?