I think it would be an opportunity to diversify the gameplay and the prospective, watching the enemies and also you teammates in first person is something refreshing, olso it could bring new gameplay mechanics, yes a sort of ''tank feeling'' where it could be fun managing the crew and the weapons onboard...I think the feeling of protection and power could be a shift compared to the normal gameplay...also driving, could be fun because more immersive...there could be a monitor inside and thus receiving communications, extra information....
Othe reasons could be for example having different kinds of missions where the crew has to capture a particular character and using the Mako to escape from the scene with inside the captive...
What about a scene where the Mako can transform itself into a superfast vehicle and surfing huge icy lands like a huge frozen lake or sea....
I think, there are enough reasons to think about a solution of this kind...cheers! :-)