This thread could get off the rails quickly. If all you listen to is guitar players that chug chug on a 7 string lord have mercy.
Long, long before guys like Petrucci copied Vai or George Lynch who used a high A string instead of a low B, folks like George Van Eps played 7 strings, and quite well might I add. A new cat to check out would be Charlie Hunter, although he is not really new. He is a newer style player that studied at Berklee and with Joe Satch. So you might think he is okay by your standards. Check him out and let me know how he compares to the inhuman Petrucci. Lenny Breau, Bucky or John Pizzarelli, on and on. The 7 string was new to rock guitar in the mid 80's but certainly not jazz. Lots of possibility with a 7 and great extensions not available on a 6. Chris Broderick is not bad either and he is from my home town... Denver. He does chug a bit but check out some of his other vids.
The allure of the axis for me is the neck carve as it is narrow at the nut...I would buy a 7 sting axis in a heartbeat. I only have JP 's because that is all ebmm offers right now and it is a damn good guitar, but the axis is my favorite ebmm guitar.