I think that's a bit different than the argument being made. We should still always use htonl() and ntohl() etc. when dealing with protocols that use network byte order (a shame we're stuck dealing with that legacy). I think even if all big-endian machines magically disappeared tomorrow, we should still do that (instead of just unconditionally doing a byte-swap).
But for everything else, it's fine to assume little-endian.
You sound like some sort of purist, so sure, if you really want to be explicit and support both endiannesses in your software when needed, go for it. But as general advice to random programmers: don't bother.