Reading your post, I think the word I'm looking for is cagoule, not anorak.
It seems so odd that this garment is missing from the wp/b outdoor manufacturers. Many cheap plastic rain ponchos come in this length, and many 'city' rain jackets (the ones that cover business suits) are at least knee length, so it's not like people would be expected to wear something unusual-looking (I would think a cagoule would sell better than a poncho, for example, for those worried about appearance).
In terms of weight, it will be heavier than an eVent jacket, but you can make up the weight savings in the rain chaps (MLD's eVent rain chaps are 3.7oz, way lighter than the 11oz eVent pants). Also, using the 2-Layer eVent should make it lighter than 3-Layer jackets, adding up to substantial weight savings over the current 3-layer eVent offerings.
This is one of the reasons I love working with cottage gear manufacturers; our voices can be heard. So who's gonna call Ron at MLD to ask for a design request? =)