Without also increasing the depth of the uppers it can make reaching the standard depth uppers difficult without a step stool. For everyday items. Set up some cardboard in front of your current base cabinets and see if you can reach your glasses and cereal. Even if you are tall and can reach the first shelf, it can be hard on your back to lean that far across the counter. And you probably won't be able to reach the second shelf at all.

If the brand your using doesn't offer increased depth uppers, or you don't want the extra cost you can also block out the uppers.
Block both top and bottom, secure well to studs. You have to cover the blocked spaced on the ends-extned side back or add a panel.

I did this, worked well. Especially good for making a regular depth fridge look recessed/counter-depth. 3" is not that much, but as jakuvall wrote you can always pull out the uppers as well (I didn't and don't have a problem at 5'6"). My 12"deep above stacked-laundry cabinet is pulled out ~15"!

Do you think pulling the base cabinets out 3" (not increasing depth, just pulling them off the wall) would make it hard to get to standard depth uppers?

Test it ... put a cardboard blocker that sticks out an extra 3 inches in front of the base cabinets and see what happens.

Thanks all. The mock-up makes it seem like I would hardly notice a difference. Co-Co, do you have any other pictures of your kitchen-- that one looked great and I'd love to see more!

In our laundry room, the cupboards over my FL washer are impossible to reach without a step stool. Also that picture you showed with the bump out behind the stove....While attractive seems to be a "grease" catcher. I am always cleaning the wall behind my cook top.

It look great, but I don't think I would want to reach over a pot of boiling water, to get the salt and pepper. Maybe something decorative there and have the shelf extend on both sides, as it is on the left?

I absolutely love the look of that too! I have never seen that done before. I keep my oil and salt/pepper behind my cooktop (between the edge of cooktop and wall there is about 2 inches) and I really love having it there. I don't mind reaching over pots that are cooking on the stove. It's just really convenient and they're out of the way.

Yes, Lavender Lass, I think I would do the whole run of the wall behind my stove, not just the one area.
I'm really digging this idea and I feel like it won't end up costing anything really. The original price quote on our quartz included a 4" backsplash that we weren't going to want, so that can be reallocated to the top of this shelf and then the tile for BS can just be broken into the two depths. I can't remember who brought up the point about making a fridge seem more built in, but that is a great point and definitely helps my design aesthetic.

Now I just have to get everyone on board who will actually be involved in creating this masterpiece! :)

If you take 3 inches from behind the stove, you lose 3 inches from the floor also. Do you have enough room in the kitchen where you would NOT miss that 3 inches?
As in the aisle width, for example....

Some of the ranges come with the shelves that you can buy to put over the stove. Is that an option for you without losing the floor space?

http://ths.gardenweb.com/forums/load/kitchbath/msg030940447656.html

https://www.houzz.com/photos/powder-room-shelf-phbr0lbl-bl~l_73266-under-range-hood

I wish wish wish we had done this, I allowed myself to be talked out of it, and first loved it in histokitch's beautiful kitchen
http://ths.gardenweb.com/forums/load/kitchbath/msg0711522912040.html

Here is a link that might be useful: histokitch's reveal