[revertts]

This is done by some apps today, though the motivation was typically network perf (http2 and then QUIC support). The stacks are large - on iOS it's difficult to take over a portion of networking without rebuilding a substantial amount of it, so you'll have TLS, a full http stack, plus all supporting logic for connection pooling, etc. The closest thing to an open-source, drop-in option like this is cronet, the networking core of chromium packaged as a standalone library. Last I looked it was multiple megabytes in size, which is still a substantial cost for iOS apps. They can also be quirky to use because they fight against the system's defaults in some areas and can cause other inefficiencies (typically outweighed by the network improvements).

I believe Uber talked publicly about adopting cronet, and Facebook gave a talk about mobile proxygen (though it is not open-source). If you pop open the Netflix and Youtube apps, you will likely see the same.