Well lets hope they make pick up items exempt from this new process.
Edited to add: Just realised the primary complaint in the OP is because the items have pick-up available, with cash on pick up as a payment option, which makes most of below irrelevant to the actual topic 
, but leaving it here in case it's food for though for others.
I have a slightly different perspective on this, and actually agree with eBay on one point - that immediate payment is indeed industry standard (for retail, at least, not so much for wholesale), and in the grand scheme of things, sellers would more than likely be able to work with it if the site.... well, worked.
The issue isn't so much eBay forcing immediate payment, it's that they way they tend to do things like this creates more problems than they solve.
I suspect most sellers, no matter what they sell, would be able to find a workable postage solution with any one of eBay's options - flat rate, calculated, or rate tables (which itself has a couple of different ways they can be set up), in conjunction with combined or promotional postage rules, and / or promotions (pricing) manager, there is a full range of options that have the potential to eliminate the need for buyers submitting orders, not paying, and sellers manually issuing invoices.
But, and there's always a big, smelly but where eBay is concerned, the above would only be true is the cart function was intuitive and worked properly, consistently. Which it doesn't.
In spite of that, though, to sellers with stores, or who list regularly, I would suggest thinking about how you would approach postage issues if you decided to sell on another site where there isn't (and hasn't ever been) an option for buyers to confirm a purchase without paying. Even just as a hypothetical thought experiement, try letting go of the sale-by-sale calculation approach and work with revenue / postage costs as single line items and see if that gives you any new ideas / strategies, because honestly, I see this as a shift that is being handled very badly (and to the detriment of all), but it's possible that sooner or later the tech issues and teething problems are ironed out and people will be able to adjust accordingly.
PS - from memory the option you can tick to allow buyers to combine multiple purchases is there so that it happens (or is supposed to happen) automatically at the checkout stage, without the buyer having to request a manual invoice. I know I had mine ticked, and set at 7 days - meaning, purchases over a 7 day period would automatically be combined, with my postage discounts applied. If someone bought another item 8 days after the first item, those would not be automatically combined, however I can still manually issue and invoice to override the setting. At least, that's the way it worked in the past, things may have (and often do) change.
