Files with aspx extension to SharePoint libraries

[Gurdev Singh]

We are planning to migrate millions of files with aspx extension to SharePoint libraries. We have run tests and found that aspx documents are rendered in browser which fits our requirements that end users can access the migrated data without any issue.

However, I wanted to check with the community if there is anything we may be missing that may trip us later. 

[#2]

Check with regular user account (without Site Collection Administrator permissions)
Also check the settings for custom script in your tenant
https://learn.microsoft.com/en-us/sharepoint/allow-or-prevent-custom-script
I expect that the sites in your tenant allow custom scripts because the aspx files open.