This is a topic which seems to inspire endless discussion; most of it pretty useful, but some of it based on logic that simply does not work; this is especially the case when analogies from cave and/or deco diving are used to formulate hard and fast "rules" for OW rec diving. For example, the bit about donating your primary because you want to make sure that the OOA diver doesn't get deco gas or a reg that's turned off....well, in OW rec diving, there's never deco gas, and there's amost never independent doubles, so that line of reasoning does not make sense. If you want to apply cave techniques (that you've been trained in) to your own OW diving, fine, but saying that they're better for OW diving (and with divers who have not received this training) because they apply to tech situations is simply false.
That said, there are lots of things that tech divers do that can benefit rec diving, and I think a slightly longer hose on whatever reg will be donated is one of those things. Regardless of your donating technique or manner of dealing with an OOA diver (hanging on, or keeping your distance) having more hose to work with will never be an impediment.
But, a bungied alternate on a really short hose could turn into a problem, because it assumes that the OOA diver will go for the reg in your mouth. Most OW divers are trained to go for the alternate when OOA, and so it's perfectly reasonable to expect some OOA diver to grab at the donating diver's bungied alternate; after all it's not far from where PADI trains you to keep your alternate. If you're tech or cave diving with other divers that know all about the bungied alternate, fine, but less than 1% of regular OW divers are going to know what this is.
One aspect of rec diving that must be considered in the great air-sharing debate, particularly in a resort area where there is a high percentage of divers with little experience and/or poor skills, is the unpredictability of those around you. So, I think it's probably best to have a set up which will allow you to successfully donate either primary or alternate. Personally, I have a standard length hose on my primary and a slightly longer (I think 36") than average on my alternate, but I'm considering going for 48" on that. If I were to get mugged for my primary; okay, it's maybe a little tight, but acceptable, and if an OOA diver comes at me asking for air, I can easily give him/her my alternate which is attached to my right chest D ring with one of those "bungie clips" that release the reg just by pulling, and there's a comfortable hose length for us to ascend together with.
BTW, it's fine to discuss an air sharing plan with your buddy, and if you're only diving with a trusted buddy, great. How about all those times you're in a resort area with a bunch of "just out of the OW class" "never did anything like this before" crowd? Those scenarios are hard to avoid if you want to dive in some of the more beautiful tropical locales, and I suspect they're also more likely to produce any sort of OOA situation, considering how many divers there are in close proximity, many with rental gear, etc.
