Hard-case suitcase, that doesn't open at the side

I think your main question is, how to access the contents of the bag, without having to split it open, thus minimizing the space required to access internal contents.

The design of these bags is for maximizing the interior space, which is why almost all open in the same clamshell fashion. They are primarily designed to safely carry the contents inside and quick access is not a top usability priority.

A bag like the one you describe could only come with an accordian-type opening on the top so that you can perhaps access the contents of a smaller compartment. Having the entire bag accessible while upright is not possible as the contents would tumble out due to the orientation.

There are some "hybrid" cases, but I question the practicality of these.

Here are some examples:

(From the floatti kickstarter campaign)

(Enkloze X1 Carbon)

(Sienna 21" Hybrid Garment Bag)

Samsonite has an excellent case (in their Lite-Box series) that offers the same space in both the lid and the base:

To lie it flat on on side, to simply open the top (like a can) takes the same amount of space as splitting the bag open, since you can open it 90 degrees. Having a specific case like that would eat into its practicality - of course there are specialized cases that are designed to be loaded and used upright. My favorite of these is the 1440 by Pelican, which looks rather rugged but it is extremely reliable:

(The Pelican 1440 (with optional internal organizer))

Victorinox Spectra answers the question exactly:

The middle zipper is for expansion.

I’ve been looking for the same sort of luggage myself, and I’ve found one I like. Checkout the Delsey Shadow luggage.

https://www.amazon.com/25-Inch-Expandable-Spinner-Trolley-Platinum/dp/B00VISP3F0/ref=mp_s_a_1_6?ie=UTF8&qid=1547535767&sr=8-6&pi=AC_SX236_SY340_QL65&keywords=delsey%2Bshadow%2Bluggage&dpPl=1&dpID=41gk4Sm1pUL&ref=plSrch&th=1&psc=1

In Spain, I purchased a hard-sided soft-top bag with the zipper where your yellow line suggests. But I bought it at a chino—a store that has all kinds of things low cost, and mostly low quality. (Spanish call them chino because they are always run by people who look Chinese, but at least one I went to was Vietnamese.)

Cost €30 for the largest size (bigger than most airlines’ check-in limit), and after one cruise and a plane flight, the plastic that made it hard-sided is in at least a dozen pieces, and part of the roller frame has come apart. I only needed it for one trip, and expected it to be worth three trips, but obviously I overestimated. If it were made of slightly better materials, it would actually have been a very good bag.

Unfortunately, all branding information was a single logo stuck on the front/top which fell off on the way out of the store. But they had four or more sizes, from this giant down to under-seat size.