Good luck with that one.....just a response from a code panel member....By FMC I mean Flexible Metal Conduit (NEC 348). The specific application I find this in is beneath raised access floors in data centers. Although the cables may be placed directly on the floor, occasionally owners prefer to utilize cable tray for better organization of systems. Here is an example (image page 10 of 16):
http://www.pducables.com/media/wysiwyg/downloads/PDU Cables 2016 Brochure.pdf
Thank you for entertaining my idea. Proposed language:
392.10 (A) Wiring Methods. The wiring methods in Table 392.10(A) shall be permitted to be installed in cable tray systems under the conditions described in their respective articles and sections. WIRING METHODS CONSISTING OF CONDUIT OR TUBING SHALL FOLLOW THE SAME CONDITIONS AS MULTI-CONDUCTOR CABLES FOR THIS ARTICLE.