And since you won't be able to modify web pages, it will also mean the end of customization, either for looks (ie. DarkReader, Stylus), conveniance (ie. Tampermonkey) or accessibility.
If this is about blocking ads, how will this stop people using DNS based ad blocking? Been using control d for awhile and it's been great. Use their DNS on my router and every device in my house is ad free.
Won't work if ads are served on the same domain name as YouTube does. Also I think the website just wouldn't load if you block the domain checking the integrity (which will probably be done on the same domain as the website you attempt to access)