I assume it's now possible because they allow a plug-in for EndNote.
"Add citations to your Pages document with the EndNote plug-in; Learn how to install and use the Pages EndNote plug-in to add citations and build a list of references." https://support.apple.com/en-us/HT204395
https://www.apple.com/feedback/pages.html
"Add citations to your Pages document with the EndNote plug-in; Learn how to install and use the Pages EndNote plug-in to add citations and build a list of references."
https://support.apple.com/en-us/HT204395