It was not obvious that replaced ICs would be recognized by the OS. And I bet they won't be recognized by the next patch. Just like you can't replace SSD chips on the current MAC devices.
Apple probably did not think people are crazy enough to try that, but once advertised as possible, they will surely block it.
They replaced the RAM and SSD from low configurations to a higher configuration
which is one Apple offers. It’s no surprise at all that it works.
While Apple certainly has the size/volume to commission custom memory and flash memory ICs, it makes little sense to do so, given the inherent impracticality of replacing fine-pitch BGA chips.
The main hurdle to replacing soldered SSDs in most Apple hardware (something only even attempted for data recovery) is that the contents of the SSD are hardware encrypted with a key that doesn’t travel with the SSD itself. The flash memory chips themselves are standard AFAIK.
The components that really are tightly integrated, with lockouts, are everything having to do with
1) security, including the SSD controller, Touch ID and Face ID sensors, etc. It does make third party repairs far more difficult, but does make a ton of sense in the context of building a hardened hardware architecture, which Apple very vocally has been doing.
2) safety, especially batteries and chargers. (As a company, do you want the bad press and potential liability caused by a low-quality third party battery or charger literally killing someone?) Even so, Apple doesn’t disallow third party chargers.