DEPRECATE.md: remove hyper after February 2025

Closes #14492

docs/DEPRECATE.md

@@ -23,6 +23,36 @@ and use TLS 1.3, or else it is not good enough.
 As of May 2024, the libraries that need to get fixed to remain supported after
 May 2025 are: BearSSL and Secure Transport.
 
+## Hyper
+
+Hyper is an alternative HTTP backend for curl. It uses the hyper library and
+could in theory be used for HTTP/1, HTTP/2 and even HTTP/3 in the future with
+curl.
+
+The original plan and goal was that we would add this HTTP alternative (using
+a memory-safe library) and that users could eventually build and use libcurl
+exactly as previously but with parts of the core being more memory-safe.
+
+The hyper implementation ran into some snags and 10-15 tests and HTTP/2
+support have remained disabled with hyper. For these reasons, hyper support
+has remained tagged EXPERIMENTAL.
+
+It is undoubtedly hard work to fix these remaining problems, as they typically
+require both rust and C knowledge in addition to deep HTTP familiarity. There
+does not seem to be that many persons interested or available for this
+challenge. Meanwhile, there is little if any demand for hyper from existing
+(lib)curl users.
+
+Finally: having support for hyper in curl has a significant cost: we need to
+maintain and develop a lot of functionality and tests twice to make sure
+libcurl works identically using either HTTP backend.
+
+The only way to keep hyper support in curl is to give it a good polish by
+someone with time, skill and energy to spend on this task.
+
+Unless a significant overhaul has proven to be in progress, hyper support is
+removed from curl after February 2025.
+
 ## Past removals
 
  - Pipelining