First let me say that I know absolutely nothing about THs but I am familiar with both bicycles and wood working. The threaded inserts with external threads are pretty fierce and will be able to take a lot of stress, both lateral and up and down.
I do not have any idea about the composition of the floor of a TH, so I can't make definitive statements but the threaded insets are going to be questionable in OSB and MDF. Neither one of those are very resistant to putt through, very slight over tightening of the bolts placed in them will damage the threaded area of the wood.
I do think your idea is a great one and I welded up my own for my pickup bed back in the 80's.