It's a pity that you don't have access to non-public sources / documentation, because that is exactly what's missing at the moment. I am quite sure there are quite a few registers that nobody outside Espressif know they exist (and that are not related to the wireless phy). For example the memory addressing and caching ("poor man's MMU"

The other stuff, the source versions, I am under the assumption they're not really drop-in replacements for the precompiled binaries, I also don't recall having seen sources of the espconn functions, but I will check.
I once had a look at LWIP itself, but deemed it far too complex for the simple tasks we usually do on the esp8266, the espconn implementation is sufficient.
Thanks,
Erik.