This was delivered earlier this year. An excerpt of the release notes details:

Export Translation Memories based on filters  

You can now run filtered Translation Memory exports from the Translation Memory view. This enables use-cases such as only exporting Translation Units created by a specific user or within certain time periods.

To define filters, open the TM in the TM Maintenance view and create and save a filter. You can then use that filter in exports. 

Note: Filters are specific to the user that created them. Only filters created by the logged-in user will be available when exporting Translation Memories. It isn’t currently possible to share filters between users.