> When programming, it is still important to write code that runs correctly on systems with either byte order

What you should do instead is write all your code so it is little-endian only, as the only relevant big-endian architecture is s390x, and if someone wants to run your code on s390x, they can afford a support contract.

Outsourcing endianness pain to your customers is an easy way to teach them about segfaults and silent data corruption. s390x is niche, endian bugs are not.

Network protocols and file formats still need a defined byte order, and the first time your code talks to hardware or reads old data, little-endian assumptions leak all over the place. Ignoring portability buys you a pile of vendor-specific hacks later, because your team will meet those 'irrelevant' platforms in appliances, embedded boxes, or somebody else's DB import path long before a sales rep waves a support contract at you.