Posted By:
warshawlawIn classic weasely lawyer form, I speak out of both sides of my mouth 
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On the one hand, there is little likelihood of large accumulations of rare pre-1930 cards from hidden old time collectors coming to light. The old time collectors were joiners and corresponders. We know who they were and what they had because they were engaged in a social hobby where exchanging information and conversing with friends was the overriding fact of life. They published, discussed and were generous with their time. They are also nearly all dead and/or done with the hobby, and their stuff has emerged and been sold into the hobby. Remember, these were eccentrics who collected old throwaways from cigarette packs and chewing gum, not "investors". Even as little as 30 years ago the hobby was in such an unorganized state, relatively speaking, that people would just as likely hand you boxes of old cards for free just to get rid of them when they learned you were a collector. I got large chunks of my collection that way. The old collectors were also just as likely to try and sell off or trade off their doubles to get stuff they needed. The odds of some old time collector coming up with six sets of E107s are minuscule simply because old time collectors by and large did not hoard duplicates, they used them.
On the other hand, there has been enough publicity and enough growth of collecting that there are undoubtedly great collections out there belonging to younger folks who accumulated them from say 1980-1990. These collections could, if collectively unleashed, add a large supply of cards to the market and depress prices. These collections are not likely to see the light of day for decades, however, until the collectors die and their heirs sell them off.
I think the most likely source of new cards would be a non-hobby source like the E107s Sotheby's had, the CJ set that sold for $800K, Dave Levin's N172 find, The T226 near set that 19th Century Only had, etc. There is still a lot of junk in trunks out there.