1. Marine could infiltrate Wano / Onigashima discreetly waiting for their chance.
2. Capturing a KOed Monkey D. Luffy means 3 things :
- ZKK is more probable than ever
- Straw Hats and allies have a reason to go save their captains when it was often the other way around
- The Marine control one of the main assets of the fight, they could ask for Straw Hats cooperation or even post-pone Wano fight : unexpected event :
Kaidou and Straw Hats allies to go invade Marineford
1. Yeah could be true that they are waiting there to invade wano.
2. a) No it won't be more probable but the reverse actually. ZKK can happen only after kaido fight with luffy. Zoro is very strong but he is still weaker than luffy as he is the main character.
b) It will be a futile attempt as they can't just teleport out of wano. They are already pretty tired after fighting Kaido army.
c) This could happen only if Garp/Coby or Fujitora arrives. Besides SH will need a very powerfull ally to even the scales otherwise marines could just kill luffy instead of taking his crew's help.
3. Anything u said could happen as I am not Oda and only he knows for certain how it will unfold.