The replacement has already happened. It is HTTP and JSON for 99% of the software developed today. The reason C stayed has multiple reasons but most obvious ones are for me are:

- People just stopped caring about operating systems research and systems programming after ~2005. Actual engineering implementations of the concepts largely stopped after the second half of 90s. Most developers moved on to making websites or applications in higher level programming languages.

- C hit a perfect balance of being a small enough language to grok, being indepedent of the system manufacturers, reflecting the computer architecture of 80s, actually small in syntax and code length and quite easy to implement compilers for. This caused lots of legacy software being built into the infrastructure that gave birth to the current contemporary popular OSes and more importantly the infrastructure of the Internet. Add in .com bubbles and other crises, we basically have/had zero economic incentive to replace those systems.

- Culture changed. We cared more about stability, repairability and reusability. Computers were expensive. So are programmers and software. Now computers are cheap. Our culture is more consumerist than ever. The mentality of "move fast and break things" permeated so well with economic policy and the zeitgeist. With AI it will get worse. So trying to make a real alternative to C (as a generic low level OS protocol) has reduced cultural value / optics. It doesn't fill the CVs as well.

It doesn't mean that people haven't tried or even succeeded. Android was successful in multiple fronts in replacing C. Its "intents" and low level interface description language for hardware interfaces are great replacement for C ABI. Windows' COM is also a good replacement that gets rid of language dependence. There are still newer OSes try like Redox or Fuchsia.

C99, but with a million macros backporting features from newer language versions and compiler extensions. Lovely features you don't get with ordinary c99:

free_sized

#embed

static_assert

Types for enum

Alignof, alignas, aligned_alloc

C was never a gateway to any flavor of Pascal, a "police state language".