Are tailcalls fated to come in second place on every feature priority list?
Let's gather the use cases and consider the implementation.
(Note: This page is about "hard tail calls" as defined in the Rose blog. Soft TCO is already in many compilers, but does not have a strong effect on software architecture.)
multi-core task distribution
(Doug Lea) chaining task execution; without tail calls you blow the stack needlessly
languages with guaranteed TCO
These are languages with functional patterns, including Scheme, Scala, F#.