Extra joints would be a compatibility breaker for sure, however the bigger issue would be what it'd do to the body itself. For instance having 2 joints in a wrist would make it twice as long - and also twice as weak since joints break relatively easy at that size + damage does transfer down the solid bones between them; hit the forearm and boom both the wrist joints etc.

The same would apply to other obvious candidates for it like the neck (another extremely weak joint) and to a surprisingly worse degree - the shoulder - which would look pretty comical with a pec -> shoulder A -> shoulder B -> arm combo.

The better solution would be single multi directional joints, but then you're looking at changing a control system that some people have been playing with for 10 years now, not to mention doubling the force a joint exerts on itself, and I'm pretty sure all seasoned players know that joints can & do break themselves with too much force just from moving.

/shrug.

Best get your thinking caps on to figure out a way of making this sort of thing work if you want to push for it.