.mogrt support in Libraries
Seems .mogrt files are not supported in Libraries. When will this be available? It's an option when exporting from AE but they don't show up. When trying to manually import into a Library I get the attached error message.

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Mogrts can be exported to CC Libraries from AE, and can be added to Libraries in Premiere as Jonas mentions, but Mogrts cannot be used natively in After Effects. That's why you'll see them greyed out in the Libraries panel in AE.
There is a workaround to open / unzip them in AE if you have the .mogrt file itself.
1. Launch AE
2. Use File > Open
3. Select the Mogrt file
4. Follow the dialog that pops up and asks you what folder you want top extract the project to
and boom you've got the .aep
Every Mogrt has the related .aep inside -
Jonas Almeida commented
Libraries do support mogrt.
Workaround is to add them to PR and ask to 'Copy to Library' where you'll have the option to better organize in you CC Apps 'Files' tab -
You can’t import mogrts using the Libraries panel in Pr or Ae. You need to export them to a Library or use the Install MOGRT button EGP and then Copy them to a Library from there. Also, you can’t use mogrts in AE so they don’t show up in Ae's library panel as enabled.