Don't worry about getting a monster truck. If the developers don't make one, there will be a billion from the community. Monster trucks are pretty popular, so I guarantee someone will make a decent one (not a "my first vehicle" type of monster truck).
A one which is fully destructible just like the other cars currently out. would love to land too hard or something and snap the axle or bounce over.
I could imagine the flex bodies on the large tyres being beautiful during jump/landings ect +1 on that idea
They will be create-able but the system will take a while to learn. You might want to learn a little from ROR before Beamng comes out. From my understanding they have similar systems but not identical.