It is quite doubtful that I am about to implement such feature soon.
The way you can work it around is the following
1. Export Collection A in Excel format from Cards|Export|Export to Excel
2. Export Collection B in Excel format from Cards|Export|Export to Excel
3. Use the Excel compare tool to compare two the .xsl files.
You can give a try with
http://www.xlcomparator.net/
I hope this can help you.
You can also try exporting to plain text and compare with tools like WinMerge (
http://winmerge.org/).