Can a double rear derailleur work? I was wondering instead of a long cage rear dearailleur (RD), what would happen if 2 rear short cage RDs were used instead?  I realize the 2nd one might cause some mounting issues but assuming there was a proper bracket to hold it in place, could they somehow be synchronized to pad out or take up similar amounts of chain but about half each so they don't need to angle as much as a single?  For example, if the same cable passed to both of them but there were calibrated to shift one rear cog each laterally, but individually would only take up or pad out enough chain for half a shift, so that combined they would make a complete shift but with half the travel/deflection or whatever the proper term is when it moves.  If they were both identical RDs (with same spring tension), would they automatically share the chain takeup/padout equally (half each) or would the system be biased more towards one than the other?

I am not suggesting this is a good thing to try.  I am just asking if it is possible and what problems may occur as a result and if it would actually work.
The reason why the RD has that bend in it is because it is what tension the chain in every single cog in the cassete. Also if it does somehow work. The length of your chain will increase, because it will have 2 cages to go through.