D&D for me was (and is ) the Moldvay/Cook B/X boxed set series. Yes I had the three core AD&D books and we used them and played them but If asked to choose between the two system, I would vote for the simple clarity and presentation of B/X. I always felt the B/X rules were more open to change and frankly in their simplicity, were just more fun to play.
So after spending a few hours this morning working on spells and wizard classes, I sat back and cleared my head by watching some spring training baseball today. (Good Lord above I LOVE this game!) An epiphany hit me in the top of the 5th, I was guilty of doing what I hate in AD&D and most similar game rules: I was trying to codify and box it all in for you, limiting it all with rules. THIS is what a Witch Hunter is...THIS is what a Shaman is...THIS is what a barbarian is...yada yada yada. What I really need to do is just write down and give YOU the basics. You are going to make the game better for you than I can. I need to get out of the way and let you do it.
No that does not mean all the additional classes and such won't come out, it just means it will be an optional booklet should you wish to add them in. Not sure I'd call them Expert or Advanced options, because that is not their scope, maybe Veteran's Manual is closer to the mark, for folks who want a higher degree of specialist and specialization in their game. Fully compatible no extra rules to learn really, just a lot of specialists kept out of the core rules booklet to facilitate ease of learning and play.
So what does that mean for you? Well it could lead to the Sword and Shield Core Rules book being done by the end of March. The Veteran's addendum could be a month later in late April or early May.