I'm still holding out hope for a "starter set/box", with additional modules/modes of play to direct the game in the variety of ways people want to play, a la BECMI (or at least B, E, and a C/M mash up) so I would be more than happy for the initial release to only go to level 5 (I do think the B/X, BECMI, 1-3 "Basic" is too few).
So I voted "Other."
I want to start at the very beginning and see how it goes. Getting from 1st to 5th level gives everyone (new and old players and DMs) a nice easy taste of how things will/should progress. Not to mention keeping page count down in the initial books.
If you get to level 5 before the "Advanced" material comes out, you should be able to easily extrapolate how to continue beyond that on your own.
That said, but in the same vein, going to level 10 would be a nice round figure that could be considered the "end" of the first "tier" of play. You get to 10, build your fortresses and retire from adventuring life a happy wealthy lord.
Then, the "Advanced" hard cover material can go, I would say, up to 20. Which itches the scratch for those who want to play "high" level (meaning, for the purposes of this hypothetical post, 10+). With details for players and more info for DMs on how to effectively create and run
challenging adventures of that caliber (not just, "Ok so, you're going to go kill this god" kind of stuff).
If they don't do that boxed/tiered route, or even if they do but also have the "Advanced" materials coming out in the "holy triad" of hardcover books, then yes, 20 all together in separate Player/DM books makes sense.
Then a later/additional book with the more complex optional rules and modules for 20+ "epic" play...which as someone here stated strike me as 'Just how many people really do this/get there?".
A "Dungeons & Dragons Highlords/Masters of the Universe" kinda book...preferably with the info for Players and DMs in the same volume...Followed up, naturally, with the additional mataerial of a: "Creatures of Legend" monster vault, containing all kinds of incredibly rare and impossible-to-beat critters and extra-planar entities, a "Lords of War" supplement for non-caster types and full on tactical/country creating/world conquering type wargames play, and a "Tome of the Archmagi", with all of the rules and listings for "epic" level spells, caster classes, magic items, and the creation thereof.
<comes back down out of the clouds and the point of the post> So, yeah. 5th or 10th level in the first release material works for me.
--SD