I share similar worries @xpilar

ps.
I wonder if we will witness and large stakeholders will dump their STEEM right after airdrop on new HIVE chain will take place

The truth is, that if old witnesses will power down right away and dump their steem - then they may damage part of Justin investment and make him lose out little bit. But it's most likely just a small % of his porfolio.
At the same time all of us, those who invested their live savings into steem will suffer the most. Our investment will be crushed, without much of a chance to do anything about it :(

In my opinion blocktrades and other large accounts, who will build their fortune on migrating community to new HIVE chain - they should wait a bit with dumping their steem tokens. To allow others to do it as well. Just my 2cents.

Yours, Piotr