Likely Stab Trim Runaway
Having flown both CRJ's and SE-DUX in its post cargo mod, I have to agree with the Stab Trim Runaway hypothesis. I haven't flown a 200 since 2011 but I know there was an SB or AW published after a couple of runaways in the U.S. a few years back. Whether DUX ever had it done will soon be revealed.
If I recall correctly the loads from OSL to TOS cubed out before they weighted out and were very well secured with a very simple system. In level flight or even in a normal 3 degree descent, the chance of trolleys coming loose was next to zero.