YAGNI only works when the cost of being wrong is low. In most software, if you do end up needing something later, you can add it without too much trouble. In hardware, it means you need to spend a ton of money on redesign, and then wait years (or decades) for people to upgrade their equipment.
In hardware, if you can reasonably foresee the need for some feature in the future (where "future" could even be > 10 years), and adding it now doesn't blow out your cost budget, you should probably add it.
Not just hardware - for the internetworking layer, you're creating a standard that everything has to follow. Extensibility is super important, but so is pre-specifying everything that a minimal implementation will have to support in 10 years.
The longevity of network stuff is a stronger argument for simplicity.
The cost of being wrong in the direction of excess complexity is higher than the cost of being wrong the other way. Layers are added, never removed. A deficiency can be fixed by adding something. A misfeature or ugly hack is a boat anchor we lug around for eternity.
In hardware, if you can reasonably foresee the need for some feature in the future (where "future" could even be > 10 years), and adding it now doesn't blow out your cost budget, you should probably add it.