Now I love the Idea of Bolt completely obliterating the WR too, but you have to be realistic. The OP wanted to give facts to support why Bolt has a LOT of work ahead of him if he even wants to touch MJ's 400 WR time. I've probably posted on this subject 10 times already, but people need to realize that the 400 is not just a "sprint" in it's simplest terms, it's a speed endurance event. Even the the 200 is somewhat a speed endurance event, as MJ's closing 100 shows.
MJ actually set that 200 meter WR while focusing SOLELY on the 400. He wasn't a 100 meter runner gone 200, or 200 runner gone 400, but a 400 runner going down to the 200. When he set that 200 record, he had not even broke 10 in the 100 yet. Not necessarily just because he was slow, but for two reasons. 1) He didn't waste his time working on pure acceleration like the 100 runners do, he focused on MAX speed and speed endurance. He was a very fast guy with a lot of turnover, but it would have given him limited gains when it comes to the 400 (or even 200 for that matter). Just as a distance runner cannot run 140 miles per week at marathon pace to gain aerobic fitness while also doing 2-3 hard V02 max sessions, a sprinter can only train certain aspects of his race as well. Training for acceleration would have limited his ability to get to top speed, or to hold a fast speed. 2) His body was obviously built to accommodate longer length sprints. He did work on his acceleration to a point, and if he was good at that it would have shown more results in his 100 meter races, but it didn't. People think Bolt is a 400 meter runner just because he ran a good time when he was younger. 45.xx is really good for a 16 year old, but what would you say is better, 45.xx or 19.xx? The answer is clearly the sub-20, as not many people in the world are capable of that. So while Bolts strengths begin to show as the distance gets LOWER, MJ's strengths showed as he went LONGER. He was just built for the 200/400.
One last thing to mention about MJ, during his 19.32 WR, he did not have an optimal race. It was actually far from optimal, he just happened to be in amazing shape at the time. He stumbled out of the blocks pretty substantially, causing him a slow start, slow first 100, and ultimately a slower max speed than he would have been able to attain otherwise. You can even see it on a video on youtube if you get a good angle, usually they are taken from very high up though.
This being said, MJ's 400 record is safe for a WHILE. Bolt is very quick over 200 meters, but it will take a lot for him to drop OVER 2 seconds off of his current personal best, and we may never see him come even close.