A bit of a blast from the past, I'd say, with Carlsen today (vs. Keymer) playing an old favorite of John Emms: 6. Bc4 e6 7. a4. The continuation was 7...Be7 8. 0-0 0-0 9. Be3 Qc7 10. Qe2 Bd7 11. a5 Ng4(?) 12. Nf5. I wonder if Carlsen had something in mind if Black had just played ...Nc6 on move 7/8/9 and been content to follow e.g. Emms-Grischuk 2000, given in old books as equalizing.