Make promotion section more hypothetical

Author: ecstatic-morse

text/0000-inline-const.md

@@ -336,14 +336,7 @@ It would be possible to allow the syntax `const expr` for an inline `const` that
 consists of a single expression. This is analagous to the single expression
 variant of closures: `|| 42`. This is backwards compatible with the current proposal.
 
-Eventually, I would like to try making any expression that could possibly panic
-ineligible for implicit promotion. This includes *all* `const fn` calls as well
-as all arithmetic expressions (e.g., `&(0u32 - 1)`), which currently work due
-to [the way MIR is lowered][arith-assert]. Even though bitwise operators can
-never panic, I would also stop promoting them to be consistent.  This would
-have to be done at an edition boundary. We would only do promotion for
-aggregates, literals, constants and combinations thereof (**@RalfJung** notes
-that this is the subset of the language valid in patterns), and
-`#[rustc_promotable]` would be ignored by later editions of the compiler.
-
-[arith-assert]: https://github.com/rust-lang/const-eval/issues/19#issuecomment-447052258
+At some point (an edition boundary?), we may want to narrow the scope of
+expressions that are eligible for implicit promotion. Inline `const`
+expressions would be the recommended replacement for expressions that were no
+longer eligible.