And double that.
Because the customer pays to random generated address , then seller has to collect all coins in one place.
While it might look small , it will be enough for a lot of miners to exclude a lot of transactions just to have their solved block accepted first and a lot of miners would not even think of including 4MB of transactions in one block.
Actually, it would not have to be double that, they could all send the bitcoin to the same address. Or, once a day, one large transaction is created which consolidates all of the bitcoin in one address. There would only be a massive transaction fee for including so many inputs. Double the transactions is not necessary.
We are seeing this already with the transaction pool running in thousands and miners adding only <100 in their solved block.
Where are we seeing this? I don't see anywhere where miners are dropping transactions because there are too many. I see them dropping transactions for low or no fees. Miners are definitely not adding less than 100 transactions in a block. In fact, there are between 500 and 900 transactions per block on average. I don't know where you are getting that number,
but I suggest you do some research before posting.