Debates about the "stack" rage every couple of years on comp.lang.c. Invariably people conflate two different meanings: (1) an abstract data structure with LIFO ordering semantics, and (2) #1 implemented using a contiguous block of [virtual] memory.

The semantics of automatic storage necessarily imply #1, but they do not require #2. Indeed, there are widely used implementations which implement #1 using linked lists (e.g. IBM mainframes, and GCC's split stacks or clang's segmented stacks).

Similarly, function recursion semantics necessarily imply #1 for restoring execution flow, but not #2. In addition to the examples above, so-called shadow stacks are on the horizon which maintain two separate stacks, one for function return addresses and another for data.[1] In the near future a single contiguous stack may be atypical.

[1] Some variations might mix data and return addresses if the compiler can prove safe object access. Or the shadow stack may simply contain checksums or other auxiliary information that can be optionally used, preserving ABI compatibility.