Thanks for your question. If NewPoWBTC were to actually exist August 15 the mining hardware of the professional miners would theoretically become obsolete and cpu/gpu mining at home would become a thing again. This would mean that the mining power would go back to the people theoretically speaking. However since segwit locked in 4 days ago it's almost certain this event will not occur. The hardfork part of segwit2x could potentially create Btc1. That would mean that some miners wouldn't update their software to support a big her block size. How and what exactly might happen is still open for debate since the hardfork is scheduled to be take place sometime around 22-23 of november.
What do you mean by unloading? I'm assuming you mean selling their bitcoin. It doesn't matter theoretically speaking they can unload it at any given time. Segwit is just a software update.
Many thanks, I suspect btc1 will be created and another round of funny bussiness will occur as it had with bitcoin cash.
To me segwit seems a means for quicker sales, aka sell all their holdings while the regular userbase doesn't have access to the exchanges. It happened with the bitcoin cash fork where coinbase and others didn't allow transfers. Bitfinex gave like a .3bch:1btc ratio after the fork too after it was all said and done, robbing from the userbase.