The "buy it now" option only helps a bidder who can't always be on line, it doesn't help the seller at all since the seller would rather get the highest bid (that is unless he just can't wait for the sale to occur. But if that's the case, then it would be better to suggest giving a seller the option of limiting the duration of the time a player is on the T).
The bottom line reason why this is not a good direction to go: If you're willing to "buy it now" at a certain price, and you think it's the right market value offer, just bid that amount when you're able to be online. If someone outbids you, well you just didn't put in your best offer.
Don't ask what sort of Chunks they are, you probably don't want to know. Blowing Chunks since Season 4!