Apple used to require apps submitted to its iOS App Store to be in the Bitcode format, and they would «recompile» the Bitcode into the exact user's iPhone CPU architecture at the download time – pretty much what OS/400 does. For reasons unknown, they have discontinued Bitcode.
Contrary to other bytecode formats, LLVM bitcode is not stable, even across minor releases.
So anyone using it as bytecode format, like Apple, has to keep their own branch, and eventually it becomes too much work.
Microsoft did the same for DirectX DXIL, as did Khronos with the original SPIR definition, thus SPIR-V came to be as replacement, and recently Microsoft also decided to replace DXIL with SPIR-V.
Stability of the Bitcode format across releases is orthogonal to the functionality it provides. Given that OS/400's TIMI has been a long-running success, it is possible to put extra effort into stabilising the Bitcode format as well. Benefits would be numerous and significant, ranging from CI/CD to apps taking advantage of new or enhanced ISA extensions.
Starting by the hyped WebAssembly, which I reckonignise it is useful, only not as breakthrough as it gets advertised given how many bytecode formats have existed since 1958.