Pretty much this, and most sticker/case sales will be moved to steam market, cause its the only place you can buy and open right away
Depends on the case and stickers for low valued probally but thats already how it is. For more value able i dont think it changes as the steammarket commisions sucks and also you have no other option then buy back market items from the balance you sold.
There have been several RMT sites that where you had to send your skins to their bot inventory first if you didnt use the P2P system and the tradehold would apply on your items. So i guess this will be the way likely across the board on trading sites.
However it will effect trading regardless since you now at minimum have a 7day hold if your trading so im curious to see how this is going to develop