The pragmatics are all against rewriting the network stack, as you have thoroughly explained. Though I have a feeling of unease. The network stack implementations are lacking diversity. They improve slower than they could otherwise do. They have plenty of undocumented obscure corner cases. Developing an implementation of a [de-facto] standard requires a solid open test suite. The Web platform has one, https://github.com/w3c/web-platform-tests. Is there an equivalent suite for TCP/IP?
Certainly there are high-quality commercial testing appliances for precise performance and correctness figures. For example, https://www.ixiacom.com/products/ixanvl
