If I could design Blackmagic's next product, here is what I would make.
An analog to digital converter with the following inputs/outputs and features:
If only one of the XLR or 1/4" inputs are connected, copy that channel to both channels of the digital output. Ideally this would cost less than $500 retail.
This would allow analog signals to easily be sent to the ATEM switcher.
I don't know why I can't find this if it already exists. The closest I've found are the following:
Am I missing something or does this product really not exist?
Analog to Digital SDI converter
Analog XLR to Digital AES/EBU converter (Midiman Flying Cow 9900-40744-00)