Alright, here's what happened last time around at the i-series summer LAN (i46):
First, a few demos were uploaded to to http://www.fileplay.net/f . This was rather limited and incomplete. A few i49 demos have already been uploaded so far (winner bracket round 1 I believe) but it's probably not a place where you can ever hope to find all of the demos.
Instead, Firestorm made a massive, messy demopack containing all of the demos which were on the multiplay servers. These were not labeled, some were 5 hours long and others just contained people DMing or otherwise screwing around on the servers. He posted this on the ETF2L forums: http://etf2l.org/forum/lan/topic-22498/?recent=404025
So we'll probably get a big filedump from Firestorm at some point. The good news is that everything seemed much more organized this year, with servers having TFTrue installed, ensuring that we only get demos from match start to end, and the logs were also named properly, so there's a chance that the demos are as well (I don't know how they did that)