Document potential effect polymorphism syntax

Author: gnzlbg

text/0000-target-feature-1.1.md

@@ -238,4 +238,9 @@ the language (beyond just a simple attribute) which could lead to the
 deprecation of the `#[target_feature]` attribute.
 
 It is also unclear how any of this interacts with effect-polymorphism at this
-point.
+point, but we could support something like `impl const Trait` and `T: const Trait`:
+
+```rust
+impl #[target_feature(enable = "...")] Trait for Type { ... }
+fn foo<T: #[target_feature(enable = "...")] Trait>(...) { ...}
+```