This topic has been discussed as far as it can be constructively discussed. Anope is currently under a feature freeze so no new features until after Anope 1.8 stable is released. If the devs so choose to add this trivial feature then they will.
What you and your "in the know" buddy, that quite frankly doesn't know is missing is that when any data is sent from any server or client to any server or client, it must go from source to target over at least 1 ircd. The ircd MUST understand the traffic being sent or it will either send an error back or ignore the traffic.
In this case user joins a channel, that join request is sent to the ircd the user is connected to, that ircd checks banlists and channel modes to insure that the user is allowed in the channel, if all is well the ircd the user is connected to begins a sync proccess that includes updating channel timestamps, modes, topics and numerics (in our case 328). All that data comes from the LOCAL ircd the user is connected to, not any other ircd. AFTER the user is synced (usually takes a few milliseconds), the ircd THEN sends the join event to it's uplink server and is passed on to every server that has at least 1 user in the same channel, this is called "broadcasting". Anope will get the join message as well and then can react if needed, such as granting ops, kicking the user and setting a ban because the user matches an akick entry, send entrymsg ... etc ..
That said, Anope can be written to send 328, BUT ONLY TO IRCDS THAT KNOWS WHAT 328 IS!! Currently only 1 have 328 that Anope supports. That's bahamut. That means that if Anope tries to send 328 on the join event on an ircd that doesn't support 328, such as Unreal, then the message is ignored by services uplink server and it never makes it to the target.
To answer your original question, yes .. a 3rd party module can be written to send the channels URL using numeric 328 to users when they join, bearing in mind that this will take place AFTER the join is completed. Bahamut send this data as part of the sync process which takes place BEFORE the users local ircd informs the rest of the network that the user has successfully joined the channel.
Locked.
[Edited on 7-6-2008 by katsklaw]