@LordPanic you seem so intent on saving L2 and/or its community, even though you yourself admit that the people currently playing on p servers do not really care. They would play MUO, Aion, BDO, CabalO or whatever shit as long as they can connect there with their preinstalled L2 client.
Like literally, I could start a MUO server, perhaps one of the old ones, e.g. 0.97d, slap a NetPro-based traffic translator between it and the internet, advertise it as L2 server and BAM - I would see people in Lorencia/Dungeon/Lost Tower/etc., while they would see TI/Elven Ruins/ToI and think they are playing L2. The attacks would be a bit strange, but anyone used to how fundamentally broken the standard attacks are in l2j will not care; perhaps a bit tougher with skills and classes, but hell, these people don't care as long as you can have PvP - and the karma system (and Phonomania on the other side) map quite nicely to one another.
In other words, you will not save the community as the community does not care one bit about L2.
@etherian yes:
Prelude BETA leak (336 client)
the three C1 leaks (the english one needed throwing out the trash)
C4
rpgclub GF (also needed throwing out the trash)
GD
Ertheia
Extenders are good as they tackle common exploits (that are well known due to how horribly outdated the leaked files are) and server crashes. Everything else that an extender does, is cancer (unless you yourself specifically need that in your custom gameplay).
As for the client packets, that is easy, as explained above. I can disguise a MUO server as a L2 server (even the latest LIVE/CLASSIC/BLOODY version), so what? It is still MUO that players would be actually playing. Not L2, no matter how much advertisements would claim otherwise.
In other words, just because I would make MUO server work with IL client, that will not magically make me have a REAL IL private server.