Bolt is both insanely talented and lazy, and has juiced periodically.
To state unequivocally that he couldn't get 43.18 is very bold.
Consider that 43.18--is it a high-quality record?
It's nowhere near as good as the 19.32 was, in my opinion. Wariner and Watts were close, and Reynolds was VERY close. Over 400m, Watts was behind by only .32, Wariner by only .27, and Reynolds by only .11
When the 19.32 reigned, the closest guy was Fredericks at .34 back, then Mennea at .38, Marsh at .39, and Lewis and DeLoach at .41
400m: .32, .27, .11
200m: .39, .38, .34
To be fair, Lewis could easily have been .10-.20 closer than he was in the 200m, but the gap would still have been smaller in the 400m.
And Bolt had no problem surpassing the high-quality 19.32, so by extension he should have no problem surpassing the lower-quality 43.18
Also, it is the same individual that he would have to beat in the 400, who he has already beaten in the 200. MJ's success at both suggests that there is a reasonable degree of commonality between the 2 events. To be fair again, there may have been more commonality for MJ, whose 2nd 100m of his 19.32 is still the best second 100m ever run in a 200m, but there is still some universal commonality, especially if specific training is used, of which Bolt has done absolutely none that I can tell over the past 5 years.
So, 43.18 is a weaker record than the 200m that he has already broken in a similar event, and was set by the same athlete, who Bolt has already beaten.
Combine that with Bolt's demonstrated junior potential at 400m, and I think the potential clearly exists to break 43.18
As icing on the cake, add to that the possibility of Bolt juicing with impunity, and not only will he break the record, but he will ABSOLUTELY DESTROY the record.
Wariner 43-mid, a bunch of times? Whether Wariner was juiced or not, if he could do that, then Bolt can do 42-mid.
As for LJ, I think Bolt underestimates just how technical it is. Sure you can jump pretty far on ability alone, but that is a damn high-quality WR, set in a competition between unbelievable athletes who lived and breathed LJ for years. I think that both Lewis and Powell delivered the absolute best LJ's of which they were capable, Lewis having had that monster jump he had erased. To get anywhere near that record will require impeccable technique.
Although Bolt is The One on the track, that's not the case in the jumps. LJ guys are long and wiry. Bolt could get there if he dropped a bit of weight, however. If he dropped some weight and receded to Lewis' 100m quality, he would be better off...however, there is that matter of form.
Other guys have come close to that record, especially with disallowed jumps--Saladino and Pedroso come to mind, not to mention Lewis and Powell both having 8.9+ jumps under windy conditions.
How good is that record, considering that Beamon was there in the 1960's? Even though Beamon did it a long time ago, nobody could touch it for a long time. Plus, Beamon's was a one-off, the miracle jump that just happened to manifest in the biggest competition of his life (I wish I had that kind of luck), plus it had the benefit of altitude. Beamon's was a monster jump, an accident of circumstances. It took 2 guys dedicating their entire lives years to match it.
Could Bolt get there with, say, 2 or 3 years of dedicated training? I would bet against it, but I do think that it is possible. He would have to develop control, and dedication to training, and stay injury-free.
The 400 record is a no-brainer, the LJ record would be very difficult, IMHO.