Earlier quoted context omitted.
You will have 2 problems with this: 1) the law, at least in the US. Laws such as copyright and maybe even the CFAA have been abused to outlaw adversarial interoperability. You'd need to either practice good opsec and operate anonymously or be based out of reach of US-allied law enforcement. 2) Apple (and maybe Google too?) - they will remove any client for a third-party service unless said client has explicit approva…
Another point to show what Apple's true goal is: To kill general computing. If you buy an iPhone you should be able to run whatever app you want on it. But no, Apple knows best and will not permit you to do anything it doesn't approve of. As for the APIs being copyrightable see Google vs Oracle.
A phone is no different from a laptop, except that it is smaller and the mouse/keyboard are part of the screen. On my phone, I should be able to:
* Open an IDE and write some code.
* Compile my code (depending on the language).
* Run my code.
The whole concept of "app stores" is absurd. In 10 years, will we be denied sudo rights on our laptops? Will we need to pay a 30% cut to Apple for every program that we install, plus $99/yr if we want the privilege of building code for our own device?