You seem to pre-suppose that there is lots of room down there to move arround in and get it up to speed
There seems to be a lot of pre-supposition that an oxygen bottle exploded, when the only fact we have is that one is merely missing.
Gas tank explosions are exceedingly rare and as far as I can recall we've never had one explode in the air. The very few occasions where bottles have failed were during in-situ ground charging (which is possibly the reason why we don't do that any more.) Anyone who watched the Mythbusters going about their hilarious business would know not only how difficult it is to break the neck off a gas bottle, but how slowly it accelerates when you do succeed. Impressive it may be, but a rocket it isn't. The bottles in an aircraft are securely clamped into place in any case. When the mythbusters tried busting a bottle as in the Jaws movie, their stunt required several attempts with a 30.30 carbine to get the bottle to burst - with a dead square-on hit to the long edge. Most hits either bounced off or simply punched a bullet sized hole through which the gas escaped with a loud hiss. Gas bottles are tough.
The final point is that an oxygen bottle explosion is extremely violent. An oxygen cylinder explosion, apart from being sufficient to blow a hole in the fuselage, would certainly have blown out the cabin floor (which is simply a lightweight honeycomb sandwich) above the area. We don't see such damage.
If the investigation shows that the fuselage rupture was indeed due to an oxygen bottle exploding, then we have a very serious problem. The bottle is missing - what was its failure mode? Without knowing that we don't know how to prevent a repetition.