i actually got this idea recently while playing a humankind run
i was playing and got to the early modern era and was like
"damn i really want the industry bonuses from mughals, but i haven't chosen a single food culture and my cities were really feeling it, but i don't like playing the hau since their unit and bonus aren't amazing"

so i got this idea to make a embassy choice like arms deal where you let other empires use your emblematic unit but they pay money to build it along with production.

how it would go is like i think it should give a stability debuff, instead of -10 it would be -15 to -20

and if its a garrison, lower the stability bonus from whatever it is.(unsure i don't play every culture that has a garrison i feel stability because stay you use your capital for this, your capital is cracked on stability, at least when i play it, i usually build most of my wonders there 

there are times i have my capital at 10 attached territories and its still at 100% and the lowered stability would help against just spamming and becoming overpowered easily.
along with this idea i think it would help with multiplayer and have friendships and alliances become stronger