Hmmm, a good idea but most mods do not share any files at all. SFB_OP shares no files with OP+ which shares no files with EEK 2.1 which shares no files with NW's mission pack... right there we're up to 46+48+6+26=128MB with no files in common for four different mods.
This suggestion may only be useful for "mods" of mods like the DIP package. (which is trivial as only the shiplist differs and it copies models assumed already present in the correct locations, ah but it includes missions so you would save some there)
Hmmm, perhaps if all modders got together and packaged it all into one zipfile download in the range of 128-256MB, then when they update their mod, just have its installer update the common "mods.zip". Then have the installer call all the necessary files from the zipfile (though the zip would be at a lower compression ratio than the installers themselves which would produce a bigger download initially but then mod update installers could still use superior compression ratios to update the mods.zip file..) to install as active files for the game... the zip would need to contain an index file (xml or just plain text) that lists which files in the zip and which mod and mod version they belong to. Place the mods.zip file into the root of the OP installation folder for easy access... hmmm perhaps we could use a different file type instead of zip... rar? for better compression? or q3?
...
Only tricky part there would be the initial coordination... It is a mechanism for what you suggest but I don't think it will really save much bandwidth. Players who are frustrated by a new download for a server would still be irritated because they would need to update their mods.zip file and the bandwidth saved would be minimal to none anyway - but perhaps the illusion of efficiency would suffice...?
Perhaps a better solution is to use a sole repository/distributor (like Pestalence?) - No more individual mods posted - just submit your new mod version to the sole distributor and he could implement an update structure like above... or an annual CD release? This will tie server admins to whatever bugs are present however.
I'm not sure we're capable of that level of organisation nor would all modders necessarily agree to it.
Seriously, maybe our best bet is to start a paypal account to pay for high speed service for all those players without it? For those unable to obtain high speed service we could lobby their providers to get out there and lay the damn cable...
Basically I like the spirit of the idea, but after exploring it here I fail to see any real benefit in file size - such a plan would help with file download simplicity... one location - one file to update kind of idea.
Another suggestion is to return to the days of no installers and just distribute zip files, requiring the users to place them all manually (ah, the walkthrough headaches of old...) this would result in larger file downloads as zips but could eliminate redundancy in files downloaded, players just have to know what to do with all the files. (Perhaps a tutorial on the use of the Windows explorer is a good idea there.)
I think the real issue here is that players get into game and find they need new files to login and are frustrated that they have to exit the game, go to a webpage and download the files (especially if on low quality dial-up)
One way to alleviate the situation is to only place mods on servers with the capacity to send them out damn fast - I've found myself waiting for mods to come down from servers at like 12KB/s when I can recieve at 500... (The reason I chose fileplanet for SFB_OP - yes a 20-40 minute wait to get the file but it comes down at full speed in less than a few minutes - and RELIABLY - I'd like to note that klingon.stasis.ca has always been rock solid though not as fast as a commercial server...)
My best take on the situation is to beg, plead, grovel and if necessary steal/reverse engineer the code to the serverkits and clients and implement an internal download system like that found in many other multiplayer games.
Basically I like the idea but it may not actually save any bandwidth, just make things simpler for the player to login which I think is the real issue... Just brainstorming here, I'll stew some more on this.
Another idea: maybe some kind(masochistic) soul would be willing to break down all versions of all mods and post all the files individually so dial-up users can go and download just the ones they need?