It seems like this would still have one of the issues SSL has where it's easy to get wrong and then it's no better than not having it, except that people think they're safe. E.g. use a weak hash function and someone can write a malicious script that hashes to the same value.
Re:Intent to deprecate: Insecure HTTP
by mike_hearn on Tuesday April 14, 2015 @01:28PM
(#9375849)
Yes, indeed, and I actually suggested this on the Mozilla thread.
Authentication can be done much more cheaply than encryption (well assuming you have the clout to force a change in standards). It could be implemented as simply as <script src="baidu" hash="a84b3">. In particular such a request could be transparently cached without security concerns.