Falcon Heavy has a standard Falcon 9 Full Thrust (FT) rocket core with two strap-on boosters derived from the Falcon 9 FT first stage. What about a heavier Falcon Heavy with four strap-on boosters (or maybe three), what kind of challenges will face SpaceX? I am wondering for some possible challenges.
With 45 Merlin 1D engines ignited at liftoff it will have a higher probability that one engine failure could cause destruction of entire rocket. But would it have problems in vibrations such as Pogo oscillation even in this case where engines are grouped in five boosters, 9 per each and not being in a single core booster connected with each other all of them (such as N1 rocket with even less engines 30 but still not successful)? The N1 had more powerful engines (NK-15) and this maybe caused higher vibrations. Probably a reason that Falcon Heavy hasn't fly yet and has many delays, could be vibrations caused in launch simulation tests. The other thing, what about the center core? Would it face to much pressure from the side boosters and by the weight of a larger second stage with more engines, more fuel and a new larger interstage? Something else mabye the aerodynamic pressure, could it be an issue? Other challenges could be in other things.
What kind of challenges would face SpaceX for such a rocket?