No, I don't think Black has any real extra options. He's under no pressure and can simply play 3...Nf6 or 3...Bf5, but then he can also do that after 3.Nf3 Nf6 4.e3.
On the other hand, 3.Nf3 dxc4 4.e3 Be6 is not something I'd be afraid of. What do you play against the QGA?
Just 3 Nf3 and 4 e3 usually. It's not that I'm afraid of it but I've seen from an article that it can be surprisingly stubborn; I'd just prefer to avoid it as that will make preparation easier. As said I am fine with allowing black to develop his light squared bishop.
(Actually, I guess black could play it anyway if he wanted to with 1 d4 d5 2 c4 dxc4 3 Nf3 c6, although I've never seen it happen)
In that case you'd still need to prepare for it because you might also meet 1.d4 d5 2.c4 dxc4 3.Nf3 c6.
Playing around with Houdini and my TWIC-based database, I rather like the lines after 1.d4 d5 2.c4 c6 3.Nf3 dxc4 4.e3 Be6 5.Nbd2 b5 6.a4 Qa5 7.Be2 Nf6 8.0-0. Ra3 and axb5 is coming, Ng5 is coming, Black's pieces aren't easy to develop.
That said, I seem to recall that article too, but I have no idea where. Was it online?
Turns out Sadler's The Slav has a bit more than two pages on 3.e3, send me a PM if you want me to mail you a scan. He's looking at it from Black's point of view and focuses on 3.e3 Bf5! 4.Qb3 Qc7 5.cxd5 cxd5 and now either 6.Bb5+ or 6.Nc3. Since you're probably just going to play 4.Nf3, might not be relevant.
I often play 3.e3 in the Slav.
That being said, ...dxc4 is not critical unless white has played Nc3 already. This is the reason I believe why white usually doesn't play 3.Nc3 in the Slav.
*looking in Game Explorer*
And look at that. I'm totally wrong. After 1.d4 d5 2.c4 c6 3.Nc3 black has many options. The most popular is 3...Nf6. The highest-scoring is 3...e6. 3...dxc4 is third-most-popular, but doesn't score as well as either ...Nf6 or ...e6. It does score better than 3...e5, 3...g6, or 3...f5. One last point is that the second-best scoring option for black is 3...Bf5. Weird, huh? Yes I know that Game Explorer is not, um, is not the most comprehensive database out there.
http://www.chess.com/explorer/index.html?id=2156&ply=5&black=0
Three points in favour of 3.Nc3 are 1) in case of the triangle 3...e6, you have the Marshall Gambit 4.e4!?, 2) in case of 3...Nf6 4.e3, 4...Bf5 is still not an option, and 3) If you play 1.d4 d5 2.c4 e6 3.Nc3 you need something against 3...c6, might as well play the same thing after 2...c6 and 3...e6. There may also be some subtleties related to going into an exchange variation a few moves later.
Negatives are that 3...dxc4 is a bit more annoying than after 3.Nf3, you lose the option of playing e3 & Nbd2 against Semi-Slav setups (can be nice).
I probably forgot a few. I've played this from both sides for twenty years so I'm a bit of a move order nerd concentrated on the slav/semi-slav :-)
For me I think it boils down to, do I feel ready playing the Marshall gambit today? If yes, 3.Nc3, if not, 3.Nf3. Nobody has ever actually played 3...dxc4 against me so I don't care about that.
Starting 1 d4 d5 2 c4 c6 3 e3 of course. I normally play 3 Nf3 Nf6 4 e3, when I don't mind playing against 4...Bf5, but I'm figuring if there is nothing concretely wrong with the more passive looking 3 e3 it looks like a good practical option for me since it avoids facing the greedy 3...dxc4 followed by 4...Be6. The idea is to play Nc3 next with pressure on d5, and now I've avoided any line involving an early ...dxc4.
Any important extra options black gets compared to 3 Nf3 Nf6 4 e3? Thanks in advance.