It's the sort of thing that will come out of the blue. The best bets have to be Lara himself, Hayden, and Sehwag, players who have already made epic innings. I also reckon Gibbs could be a good bet. But it really could be any batsman who averages over 45. The reason those 3 are the best bets is because they have past experiences of that kind of innings. Lara made his 400 in April 2004 but he was also within sight of that mark when he made 375 against England in 94 and when he was storming along on 277 before he got run out against Australia. Hayden was within sight of 400 but then he got caught.
I don't reckon that the record will be made against Zimbabwe or Bangladesh. It will be made against a decent side. I don't think any of the top batsmen would want to make such an important record against a sub-standard team. It would be disrespectful to the game of cricket. The main reason everyone (apart from the few killjoys) was so happy when Lara got his record back was because it actually meant something - Hayden batted against a rubbish Zimbabwe bowling attack, Lara batted against a decent English one.
As for Lara being selfish batting to 400, well, during that match he always said that he would declare at 750, and as soon as WI reached 750, he declared. The reason WI did not win the test was because of failing to bowl England out twice, thanks in part to some bizarre fielding errors (a big one on Flintoff by Lara himself). And also rain delays didn't help. An extra 10 overs for Lara to reach 400 wouldn't have made any difference.