iFixit have completed their teardown of the iPhone 8. They found that the screen and battery were fairly easy to replace, but that the rear glass panel was extremely difficult to remove due to large amounts of glue.
https://www.notebookcheck.net/iFixit-teardown-rates-iPhone-8-repairability-as-6-out-of-10-but-glass-back-almost-impossible-to-replace.250938.0.html