I’ve read and reread the WordPress Trac ticket about this issue. I’m not certain if this is actually going to be considered a bug which requires fixing.
I just released an update to CSV Import, version 1.4.2, which address the change in WordPress 4.7.1 in a secure way which should now allow you to upload CSV files again.
This update to CSV Import will (err should) work regardless of any changes that may or may not come with WordPress 4.7.2 in regards to this issue.
Hope that helps, apologies for the trouble!
ps. If you installed the Disable Real MIME Check plugin, you should deactivate and delete it.
pss. If you see this same error in the WordPress Media Library when uploading files, then you will still need the Disable Real MIME Check plugin installed. The change I made to CSV Import will not affect other plugins or WordPress when uploading files which throw this error.