Think 11c4 is quite a decent move, it is looked at in a chapter in "Cutting edge 1" from Quality chess. Being played more often recently by top players as the positions after c3 are becoming a bit too over analysied.

ok, so 11...b4 is the move to go, then... and this 11...Nd4 seems decent only in conjunction with Bb7 instead of Bg5, interesting... ah, I guess I should definitely buy a book on Sveshnikov at some point... I made my preparations based on some scattered online materials and some GM games from the database... so I know my way quite well in some of the mainlines, but there is too much stuff out there, so it's nice if someone else already did the work of bringing it all together :)

Concerning move 11 c4: Rogozenko " is harmless requiring some knowledge from b lack. Black equalizes with b4 knc2 a5 be2 0-0 0-0 bg5."

Fritz 13 " the move KNd4 instead of b4 gives black about a .33 loss.

Mullon 2313- Tirard 2399 0-1 megadatabase 2009

Used 11 KND4 Rogozenko" immediately using the drawback of whites previous move"

In the sveshnikov reloaded by quality chess and Rogozenko most of the material concerns the c3 rather than c4 opening. He emphasizes the move b4 after c4 with a5 to equalize: Point being is that c3 is a much better move than c4 although needs very accurate play.

Yep, it does seem that early Bg5 is not good here, that's why the two referenced GM games featured Bb7 ideas instead... Of course, I was unaware of all this... but Bg5 is otherwise good in the 11...b4 line, so I thought it would be natural to try and preserve the bishop pair as part of the compensation for the material. But I guess Black can allow Nxf6 and still be fine, even recapture gxf6, reaching similar structures as in the main lines.

Houdini 1.5 suggests typical white idea 14h4 Be7 then 15Nc2 because 15...Bg4 16Nxd4 doesn't work. Probably know this already because  after 14Nc2 Bg4 15Qd3 Ne6 Houdini prefers 16Qg3 too. So white should be able to get an advantage against 11...Nd4, but looks playable.