that is called, "cool for now?"

Wouldnt that be just as unfair as for others?
I mean. if x doesnt get crushed by y's 8 stack then maybe z will or somebody else.

just kill the sucker if he don't flag. There is no benefit to keep people alive that don't flag to you.

I forgot: Humans are warm blooded. If they become cool, bury them quickly.

Why not just proceed with the truce, then backstab when you are ready for it to end?

Calling a truce is fine... you announce it to the table, the player you're trucing with have the option to accept or decline the truce, and then you deal with any repercussions of said truce.

Verbal flagging however is not fine. I know you havn't mentioned it, but often players in the scenario you describe will announce a "flag" to the larger player, thus attempting to force a "truce" under the disguise of a flag, and then expect it to be respected as if it was a real flag. It's not, obviously.

Calling a truce = fine.
Calling a vflag = not fine, ever.

As for your idea... I don't think it is required. It's luck of the draw if you get a game (or a few games) where you get owned by bad positioning. I think if you call out a truce option, loud and proud, and you can survive the wrath of all other 5 players, then that's a fair sorta game, as I mentioned above.

A cultural shift to calling 3-round truces could be an interesting idea, but you might find it hard to train everyone to understand what you're doing.

so let's say i am that bigger player and i let you live for 2-3 rounds...for what? So I can give you the chance to dice up and kill me? No thank you.

The price you pay for living, is a worse position behind the bigger player. I mean, next time I'm in back of you and want to live for 2-3 rounds so i can attack you later...I'll bring it up to you and see what you think. :)

Oni is just right. Either you truce / flag, or you don't. Just for some rounds is kinda senseless.