Thanks for a good question!

Fairly, I don’t believe the line 10.a4 would pose any problems for Black. First, let’s go back to the game Kortchnoi – Vallejo Pons, Biel 2002. It continued 10. ..b4 11.Ne4 c5 12.Ned2 Be7 13. Re1 0-0 14. e4 cd4 15. e5 Nd5 16. Nb3. Black’s position looks quite solid, the bishop on b7 and the knight on d5 are pretty good. However, his position has serious drawback – it is not so easy to find concrete ideas and to get real counter play while White has a clear plan of the K-side actions which he can prepare in safety. He does not care too much about the d4-pawn as it is almost in his pocket, and Black is often happy to give it up to clarify the position and to open files for his pieces.

Such approach is maybe new for this particular line but generally it is quite common for this kind of position – it is rather typical for Meran as well as for Queen’s Gambit Accepted. I can mention here some examples, in which White has successfully realised advantages of his position, such as Kasparov – Piket, Tilburg 1997, which was commented on the Chess Publishing or Shipov – Lesiege, FIDE WCh Moscow 2000. But Kortchnoi’s line is a different story as there White makes too many moves with his knight (Nb1-c3-e4-d2) while if we take a look at the following line of the QGA 1. d4 d5 2. c4 dc4 3. Nf3 e6 4. e3 a6 5. Bc4 c5 6. 0-0 Nf6 7. Bd3 Nbd7 8. Re1 b5 9. e4 cd4 10. e5 Nd5 11. a4 we may notice that White still hasn’t moved his knight from b1 and so in case of 11. ..b4?! he gets clear benefit. That’s why in such situation Black, if possible, usually meets a2-a4 with b5xa4, simplifying and opening the position on the Q-side as well as gaining some tempi for development since he will use the placement on a4 of any of White's pieces.

So it is hard to believe that White can get advantage, wasting so many moves for the knight’s manoeuvres. As to the line 13. Re1, perhaps Black should not close his strong bishop on b7 after 15. e5 by moving his knight to d5 – maybe he would immediately begin concrete play by 15. ..Ng4!? I briefly looked at this position and Black’s chances seem to be good. For example, 16. Be4 (16. h3 Nc5 17. Ne4 Ne3!) 16. ..Bxe4 (16. ..d3!? looks interesting: 17.Bxb7 Qb6; or 16. ..Qc7!?) 17. Rxe4 f5! 18. exf6 Ngxf6 19. Rxd4 (19. Rxe6 Nc5) 19. ..Bc5 20. Rd3 Qb6 21. Qe2 e5! with initiative. This idea has not been tried yet so maybe it’s just a good novelty?! Unfortunately I couldn’t find the NIC Magazine you mentioned so I hope very much it has not been already refuted there… 

Good luck,
Ruslan