Ok, sorry to disappoint you guys. Vivi is not ending up with Luffy!!!
And the reason is rather simple, Luffy is just a physical monster. And I mean Kaido and big mom level of monster. the only difference between Big Mom, Kaido and Luffy is that they are giants but Luffy is normal size. but the actual strength of these 3 is comparable to each other.
Vivi will simply break under the pressure and dumb Luffy doesn't know how to hold back either.
The only one who can handle Luffy is Big Mom. So invest your stucks in Big Mom X Luffy before it's too late.