If the tail-call-needing function isn't found rather quickly (say, in the first 100? frames), then isn't it unlikely that the tail call will help? That seems like a much rarer case. Is the cost of going 1000 functions deep that expensive? Most threads aren't gonna hit a high % of stack without having some sort of problem anyways.
Of course it'd be better for the JVM to support this in bytecode, just like generics, stack allocation, and pointers. But it seems to me that if there was a real solid need for TCO then a JVM could implement it with tunable heuristics (most Java code doesn't need TCO, so if your code really depends on it in complex scenarios, you can always pass a -XXTcoInspectionDepth argument.)
Of course it'd be better for the JVM to support this in bytecode, just like generics, stack allocation, and pointers. But it seems to me that if there was a real solid need for TCO then a JVM could implement it with tunable heuristics (most Java code doesn't need TCO, so if your code really depends on it in complex scenarios, you can always pass a -XXTcoInspectionDepth argument.)