This has me wondering: How would Standard play if say the victory criterion were set at say 12 SCs...?

Hm, one of the geographic aspects I enjoy about Diplomacy is that it utilizes the geographic choke-points. Sure, they increase the chances of a stalemate, but they are an intricate part of geopolitics.
I'm not sure how I like lower victory conditions as 12 in Standard doesn't even control the map by defacto. 18 is largely the stalemateline +1 or so and defacto control of the map.

And with powers threatening a solo much earlier, this also creates greater diplomatic instability.

Personally, I don't like Milan because it takes away from the Austrian-Italian relations. It takes much more negotiation, and the very thing that creates trust rapidly is also a key to treachery or the stab. I think Milan trades geopolitical instability for geopolitical stability.
It also emphasizes the threat a conquerer from either side can utilize that adds to the instability.

Personally, I don't see it as a masochist exercise; I see it as an objective with a high challenging standard.
I will say that dangling the carrot in variants certainly would help players to be weary of momentum-tempo, balance of power, and etc.