There should be 10 levels in the initial 2014 release, giving them time to get the Level 11-20 expansion book right for 2015. Then if that works well, release the Level 21-30 book in 2016.
I cannot express enough how terrible an idea I think this is, nor how strongly I feel that way.
This is a great way to lose
every single group (okay, maybe just the vast majority of them) that is currently playing above 10th level and would like to convert.
For God's sake, there is
no reason to release the game in an incomplete form.
If I run a high level game with gnome druids and half-orc barbarians fighting frost giants, there is
no reason why I shouldn't have everything I need to convert on day 1. NO REASON.
The whole crappy "let's save some mainstays for later" approach pissed off a ton of folks about 4e. You COULD NOT play a gnome, half-orc, barbarian or druid on day 1... in fact, you had to wait for a year.
Likewise, if you wanted to use certain classic monsters- REALLY CLASSIC- like frost giants, gold dragons, ankhegs, etc., you had to wait a year.
Let's not. Please, let's not.