Minty, I've wished for a long time that eBay had a way to bid on the same sellers items at once instead of having to bid individually every time. I never gave the offer idea any thought, but that would be even better. I like to buy multiple items from the same seller just to combine the shipping and save that way, so your idea would make that much easier, the offer part would be really cool too at least for BIN auctions with the Make Offer option.
I wish they would come up with something, although I'd probably regret it later on after spending twice as much as I already do if it was easier to buy that way.