...
What you are proposing is that Electrum servers store information that is not in the bitcoin blockchain.
There are more obvious uses to it than just sorting transactions. For example servers could store transaction labels.
This is beyond scope, at least for now.
It would involve an extra layer and infrastructure, and it would be a bad idea to mix such requests with the stratum commands.
That makes sense. Thanks for the thorough explanations.
I realize it's a bit of a hack, but do you see any practical drawbacks or issues in using tx_id fields for sorting transactions when their timestamp fields are equal? That seems to work well in addressing my UX concerns.