Whenever I talk with old wrenches about wheelbuilding, they always seem to talk about double eyeleted rims as the pinnacle of strength and quality. However, it seems most modern, high-end rims have no eyelets at all, let alone doubles. The only models still in production that I know of with double eyelets are basically 15+ - year - old designs (Ambrosio Nemesis, Mavic OP & A719). While the principles behind double eyelets make sense to me, and they definitely make building a wheel easier, AND they look super cool, I'm sure there is a reason they are no longer widely used. Is it because new stronger alloys and fabrication techniques make the extra weight of double eyelets unnecessary? Is it something to do with alloy nipples (I can't see how this would be the case)? Do you miss them? Do you wish they were more common in new designs? If anyone has some technical data on the benefits of double eyelets please share! thanks.
Funnily, we actually have many more new rims available with them now then in the early to mid aughts when they were at a low point and it seemed like Open Pros and A719s were the only rims with them. There are now also good DT, Araya, and H+Son rims with them, and maybe some others. They are not extinct.
The main thing they do is spread the load to both walls of the rim in order to reduce the risk of fatigue cracking. V-section rims, which have of course risen in prominence, tend to have (or can easily be made to have) a concentrated section of material at the spoke hole, which accomplishes a similar thing in a cheaper and potentially more weight-saving manner. V-section rims tend to not have fatigue cracking issues unless they're either garbage, way over-tensioned, or way under-weight for their use. For the most part you don't really see it on the nicer aluminum V type rims.
Double eyelets add weight and cost, are not immediately function-critical, and, most endangering of all, are invisible to consumers. So they have a rough time being something that manufacturers care to mess with.
It's worth noting that in a sense, when a box-section design is what you want, double eyelets actually are more relevant than ever. One of the major things that's happened with rims in the last decades is that materials (i.e. fancy niobium alloys) have gotten stronger but not more fatigue-resistant, or at least not at the same rate, and cross-sections have gotten bigger and stiffer with thinner walls. Those are some of the reasons there's more emphasis on building to a tension spec than there used to be. With a classic road rim, however much tension you added that the rim could still take structurally, you could feel safe knowing that it could also take it reasonably in terms of fatigue resistance. It was also easier to accidentally taco them in the stand from adding too much tension. There are rims running around now that are much stronger and stiffer, so you need to cap out your tension even though the maximum strength capacity hasn't necessarily been reached. From a design perspective, double eyelets can help you get access to more of that strength by adding fatigue resistance.
They can't be used with tubeless tires. From Schwalbe's FAQ on tubeless:
Tubeless mounting is usually impossible for [...] rims with double eyelets. In these cases, it is not possible to ensure airtight sealing with the rim tape.
Actually, those "double eyelets" should rather be called "sockets". They bridge the two horizontal walls, distributing the load, adding stability. See also Jobst's explanation here.
He also states:
Rims have eyelets the same as eyelets on shoes or clothing. Rims can also have sockets that bridge inner and outer walls of a hollow rim and are held in place by eyelets. [...] Eyelets are generally used to prevent galling of the aluminum rim when highly loaded nipples are turned, regardless of their material.
Socketed rims are still readily available. In fact, I just unwrapped one.
Sockets might be impractical on very deep V-shaped rims. They would need very high sockets that probably would be not sufficiently sturdy, in particular as their material of choice seems to be stainless.