If during a plan year a participant has a change in circumstances and finds the dependent care allocation is too much and medical is too little, can money be swapped between these two categories without a trigger event?

If not, is there any congressional bill in process which would allow a mid-year change in allocations without a trigger event?

I would take a hard look at the "change in circumstances" that is creating a need to change. That would be your best bet in finding a status change that would allow a change in election. Baring that, you can't swap money from one allocation to the other.
I'm not aware of any legislation that would allow additional family status changes.

The IRS views each flexible spending account election as an entirely independent election. There is no such thing as midyear mix and match in a Cafeteria Plan