The promised Dev Blog finally appeared and looks like the multi-size thing will be exactly as I expected it to be. New BPOs with lower salvage requirements and a flag controlling what size rig can be plugged into what ship class. Some of the FUD speculation on that issue was getting a little crazy on the forums.
What does this mean? It means we're going to see an explosion of rig usage. Rigged T1 frigates, destroyers and what not will make an appearance on a battlefield near you. It will be cheaper to rig industrials and cruisers/battlecruisers as well.
I suspect the most interesting un-intended effect will be that there will be a slighly different rig patterns between the large and small rigs. What do I mean by this? Just as the purpose and battle usage of the different classes of ships is different, so will their rig requirements be different as well. For example the rifter. It is unlikely anyone will seriously consider using tank rigs on it. Falloff and damage rigs? oh baby. Mobility rigs? sure. Tanking rigs are more prevalent on battleships since the objective there is to make your ship evaporate more slowly when they get primaried. This isn't realy a consideration for frigate operations. They evaporate prety quick no matter what you do, so might as well improve something that'll make a difference while they are alive.
As for all the guys whining about the researching of the new BPOs. Grow up, prefect ME on the worst rig was in the 40's as I recall, most averaged out to 20-24 with quite a few arround 10-14, so since medium rigs will be 1/5 requirement of large (current) ones and smalls 1/5 of mediums, the ME needed on these rig bpos will be much smaller than current ones. One would assume that the BPO prices will also be commenurately smaller as well. This simply means that you can bust off a whole whack of BPOs in the same 24h period if you've got your skill slots available and a high sec POS. Most serious producers have access to same so it won't be an issue past the first few days.
I will note that this is a serious buff for the newbies (always a good thing). Oh and pirates in Rifters.