RFC: Un-feature-gate if let and tuple indexing

text/0000-un-feature-gate-some-more-gates.md

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+- Start Date: (fill me in with today's date, YYYY-MM-DD)
+- RFC PR: (leave this empty)
+- Rust Issue: (leave this empty)
+
+# Summary
+
+Remove the `tuple_indexing`, `if_let`, and `while_let` feature gates and add
+them to the language.
+
+# Motivation
+
+## Tuple Indexing
+
+This feature has proven to be quite useful for tuples and struct variants, and
+it allows for the removal of some unnecessary tuple accessing traits in the
+standard library (TupleN).
+
+The implementation has also proven to be quite solid with very few reported
+internal compiler errors related to this feature.
+
+## `if let` and `while let`
+
+This feature has also proven to be quite useful over time. Many projects are now
+leveraging these feature gates which is a testament to their usefulness.
+
+Additionally, the implementation has also proven to be quite solid with very
+few reported internal compiler errors related to this feature.
+
+# Detailed design
+
+* Remove the `if_let`, `while_let`, and `tuple_indexing` feature gates.
+* Add these features to the language (do not require a feature gate to use them).
+* Deprecate the `TupleN` traits in `std::tuple`.
+
+# Drawbacks
+
+Adding features to the language this late in the game is always somewhat of a
+risky business. These features, while having baked for a few weeks, haven't had
+much time to bake in the grand scheme of the language. These are both backwards
+compatible to accept, and it could be argued that this could be done later
+rather than sooner.
+
+In general, the major drawbacks of this RFC are the scheduling risks and
+"feature bloat" worries. This RFC, however, is quite easy to implement (reducing
+schedule risk) and concerns two fairly minor features which are unambiguously
+nice to have.
+
+# Alternatives
+
+* Instead of un-feature-gating before 1.0, these features could be released
+  after 1.0 (if at all). The `TupleN` traits would then be required to be
+  deprecated for the entire 1.0 release cycle.
+
+# Unresolved questions
+
+None at the moment.