My concern with that type of mechanical device attached to an already cantilevered set of steps is the lever arm to the plywood trailer floor and frame if it is attached there as well (most are). Then the added load to the step brackets as well. Somethings gotta give. Most folks will carry an extra step just set on the ground.
I do like your design though and if you add some sort of ground support, it will work. Even for the long three step Hickory brand steps to our 5er I have a Camco gadget to help them carry the load Amazon.com: Camco 43681 Save-A-Step Brace (4-5/8"-8"): Automotive
. There is also a new one that is permanently mounted too that may be better: http://www.amazon.com/Camco-43671-Se...HCCJ4WC64Q6NHA
Dave W along with my DW, Susan and our poodlepups, Callie & Molly,2011 Ford F250 6.7 CCLB, 5er Hitch Option w/B&W Hitch,,Ride Rite air bags, 2014 Montana High Country 343RL (38')