You should think and understand the risks associated with such upgrade. What are the chances that there will be unexpected UI behaviors or JS errors from the upgrade? In my opinion, it is not safe to upgrade the jQuery for Sitecore, and below are a few points for this -
- Sitecore is a very big system and it has lots of things dependent on the JQuery. If you are planning to upgrade the JQuery you need to test the full Sitecore system which is not an easy task.
- You will never know the impact of it even after performing the complete testing.
- When next time you will going to upgrade Sitecore, you will face similar problems with the new version of Sitecore.
- It is not recommended to change anything on the existing Sitecore solution until there any specific requirement or the Sitecore team itself provided something to update.
- Make sure you will have the Sitecore support continue after this jQuery upgrade.
Based on the security guidelines of some organizations, they don't allow the older version of jQuery for pubic facing websites but you can restrict the old JQuery access for the CD sites.