Address comments

Author: ekr

explainer.md

@@ -31,7 +31,6 @@ components.
 ## Use cases
 
 The first use case to be supported by the API is the processing of encoded media.
-
 However, the same approach can be used in future for use cases such as:
 
 * Funny Hats (processing inserted before encoding or after decoding)
@@ -43,9 +42,11 @@ However, the same approach can be used in future for use cases such as:
 
 This API can be used for experimenting with end-to-end media
 encryption (e.g.,
-[SFrame](https://datatracker.ietf.org/doc/draft-omara-sframe/). However,
-having both the key and media available to the JavaScript is
-unsuitable for production end-to-end use. This API will also define a
+[SFrame](https://datatracker.ietf.org/doc/draft-omara-sframe/).
+However, this API is not recommended for this use case until a
+mechanism that allows browsers to perform end-to-end encryption
+without exposing keys to JavaScript becomes available.
+This document will also define a
 mechanism for browsers to provide built-in transformers which do not
 require JavaScript access to the key or media. Separately, this or
 some other WG may work on a mechanism for end-to-end keying.