Well, as I have seen it, you could just gather intelligence as you might, I have seen the top sum to be somewhere 75-80, a fighter can have 18/00(Str)+18(Dex)+18(Con)+3(Int)+15(Wis)+3(Cha), so that's 75.
And besides it's always easier to use Shadowkeeper(?) to modify the char for at least for a mod.
Just telling you. 
I think he's talking about something that on each reroll will show you how many
spendable points you have. Usually what I do is when I see what looks like a good roll, I decrease all attributes to the minimum allowed (which is different from class to class), and see how many points I end up with available to spend. If it's a higher number than I've seen before, I store the roll. Then I continue with more rerolls until I'm satisfied with the number of points I can spend (or just get tired of rerolling).
From what I gather, Lucas suggests skipping the point where you manually decrease all attributes, so that you can see how many available points each roll has without doing anything. While I think it's an awesome idea, and I'd love to see it myself, it's unfortunately hard-coded and impossible to do something about. Sorry.

As for Shadowkeeper - yeah, but some people prefer not to do that.