Is your concern for OW just the long hose or also the primary donate, and likely necklace? In reading the above I was not sure if by 'short hose' you meant 'I give you my octo' or just not a 5' or 7' hose.
I may be mixing concerns of a) long hose, 5' or 7', and b) primary donate with a short 40" hose. The length of a long hose definitely adds an extra restow step for the instructor that is extraneous to what OW students need to see. As a DM candidate not is a shop, it seems a 40" primary and necklaced secondary could easily teach primary or secondary donate, to match the needs of the OW students gear. If we feel primary donate is a good idea, and have an option, I'm not sure we do the students a service by only showing them what we might view as less desirable a method.
Edit: Is the concern the rigging for primary donate? Even if that is currently used as secondary donate. I.e., breathing necklace and 40" clipped of with a tear out bungee loop. And this all got debated many times. OP seems fine.
I'm still not quite sure what you want to know but I'll give you some background information and my personal thoughts about it and see if that covers it.
MOST PADI instructors are still teaching to donate the octopus. The standards do not dictate this. In fact the wording has been changed over time to reflect that donating the primary is also possible. PADI would allow the instructor to teach either and in any configuration the instructor chooses. Because of this the roles of the person donating and the person receiving air are defined to put the donator in the driver's seat once the OOA sign has been given because as receiver you "receive" a regulator, whether it is the primary or the secondary. That takes the guesswork out of it. Years ago the roles were reversed but this has been sharpened up to reflect the modern realities.
Naturally our sport is dominated by two main variations. (1) short hose primary, donate the secondary and (2) long hose primary and donate the primary. There are other configurations that use, for example things like an AIR-2 or long hose secondary among others. The point being that no matter how you do it, the configuration needs to make sense and the instructor decides the protocol (within the roles defined).
That's where the flexibility sits.
In practice, however, one configuration is much more prevalent than all the others world wide. Namely short hose primary and donate the secondary.
That's where my personal opinion starts. My thinking is that if the vast majority of divers are still using this then this is what I want to teach. Divers who get insta-buddied with strangers are *most* likely to encounter this. Moreover, donating a longhose primary will not properly prepare a new diver for the slight complication of having to swim together with another diver using a "trad" configuration. The long hose is easier, which, for me is a reason to introduce it after they understand the trad config first. I guess you can see it as being like teaching a calculator *after* but not before learning how to add.
I also only only teach the trad config in the OW course. I discuss the fact that there are alternatives but i don't confuse matters with showing them X-number of variations. i want them to automate, as much as possible, one way that they can really rely on remembering if it ever comes down to it.
Finally I believe that once a novice diver has 20 or 30 dives of experience and is getting well comfortable with their own process of diving that none of this really matters as much. Once the diver is relaxed and most skills are getting to the point of being fully automated then there will be much more free attention (and therefore potential for flexibility) available when something unusual happens.
Does that address your question?
R..