Oops, the title should say 8. Kxf2, not 8. dxc4.
5. Nxf7, 6. Kf1, 8. dxc4

Never mind. I'm now using a chess engine to analyze this position. So far, dxc4 is at least = for Black.
Possible continuation: 8...dxc4 9. Nc3 Bg4 10. Qf1 O-O-O 11. h3 Rf8 12. Kg1 Nd4 13. Qxc4 Be6 14. Qd3 Nh5 15. Ne2 Qh4 16. Nxd4 Qf2+ 17. Kh2 Qf4+ 18. Kg1 Qf2+ with perpetual.
Contributions and/or corrections are welcome.

Even better is 8. . .Bg4!! Check it with a computer. With modern engines and persistent hash tables, Black has already proved a clear draw after 5.Nxf7?!

Even better is 8. . .Bg4!! Check it with a computer. With modern engines and persistent hash tables, Black has already proved a clear draw after 5.Nxf7?!
I don't know what engine or hardware you're using but at depth 33 Komodo 9.2 has White at +1.5 after 6.Kf1, and I plan to let it go a lot deeper than depth 33. Admittedly it is relying on 6...Qe7 7.Nxh8 Bb6 for this evaluation, not 7...d5 -- I will probably let it analyze at Black's 7th move after I let it analyze at White's 6th.
A while ago, I came across this line in the Traxler:
I played Qc5+ and eventually lost. Is dxc4 a winning alternative?