At the moment pcsx2 is not able to "play" games very well (if you read the FAQ you know what i mean ) so i don't think the autors will implement it right now,they are focusing on compatibility;maybe in the future...who knows!
They most likely wouldn't be able to. Least not without breaking the law with regards to the DNAS protocol etc... Sony certainly wouldn't like anyway, and would most likely forbid it in the license aggreement if it was included in a future version of PCSX2.
Emulating the eth adapter wouldn't break anything... It would be illegal if the emulator faked the dnas info to let the users play with their games, but there is nothing bad if it only emulates the network connection. (Assuming that there is a way to read the dnas info from the disc, or dumping it using a ps2 and reading it from a file, like we do with the bios).