I've looked at some of the recent videos and scores and revised my theoretical estimate for a perfect scoring route for ships that can follow it (I'm assuming A-L/A-S and at least B-L should qualify; other ships may or may not fall a couple billion behind). Some speculation and wishful thinking ahead.
Through stages 1 to 4: up to 9 billion.
Stage 5 alone: up to 13 billion, might be more depending on the hyper recharge and activation timing.
No-miss/no-bomb/st5 chain bonuses: 1..7 billion, assuming neither additional bonuses for running max bomb multiplier through the TLB nor more expensive life cash-in for an Inbachi clear.
Hibachi kill: 6 (1+5) billion.
Inbachi kill: 15 (5+10) billion.
Theoretical maximum thus seems to be at around 44 billion for an Inbachi clear and 35 billion for a Hibachi clear, assuming perfect survival. Not particularly fond of stage 5 once again being more expensive than all other stages combined, but at least this time there's a clear scoring incentive to fight and kill either TLB.
Clover-TAC has got a 33.2 billion Hibachi clear, so I'm assuming he's got pretty close to flawless performance but lost a life at Hibachi, or maybe he used bombs for rank control throughout the game to no-miss Hibachi. I wonder if he consciously hasn't gone for Inbachi yet to earn a strong score foothold first; in real world it'd likely get him about 37?38 billion for a very high risk of losing everything in case he couldn't survive the second form. A superplay DVD, if released, would likely show 40 billion Inbachi clears with A-S and B-L. An Expert Inbachi clear would be interesting to see if only for the thrill of NMNB'ing the entire game. I bet it'd be a low-score clear, heh.