I already tried this actually a long time ago. I put metal plate inside a plate carrier and put several magnets inside a backpack so it will stick to the back just like in 1/1. The problem was the magnets weren’t strong enough and the layers of cloth/material made them even weaker. I bought the magnets from Chinese seller on ebay so that’s probably the reason.
While the ease of use is very tempting, I don’t think it will catch on with the hobbyist within us. We want to imitate 1/1 as close as possible. I suppose if Hot Toys is still making military figures, this would be the next step in their design and manufacturing process to woo the collectors who want cool looking figures but don’t want to assemble them.
And probably because shipping items containing magnets (even tiny ones) will be adding an unnecessary complications to the shipment process.