I would probably never run across one but I wonder how well the cape like the foot guards use would work. It might work fine on the square and it might work better in the woods--we will never know. It is just an alternative idea but you might get funnier looks than if you were using an umbrella. You couldn't use a high riding backpack, though, but you have the same problem with an ordinary poncho.
When I was in the US Army in Germany in the late 1960's, a few soldiers had modified their ponchos by having an army blanket, trimmed to fit, sewn inside. They were quite heavy but worked and were a good idea. But I think that would be a little over the top for backpacking.
Currently the US Army has, or did have, something called a poncho liner, which is a light nylon and polyester quilt the exact same size as the issue ponco with tapes or cords to attach it to the poncho itself, which makes it sort of like the modified ponchos I just described. Only there is no hole for the head, so the idea is not carried to its logical conclusion. Poncho liners with a hole are available commercially, however.
I do have an issue US Army parka, the current one of Gore-Tex that works very well under certain circumstances, less well under most. It is easily my heaviest garment but I don't have anything that works as well in freezing rain, which we seem to have as often as we do snow where I live. In fact I had spent a night in the woods a couple of years ago when I wish I had one. I had chosen to camp on a ridge, mainly because it was the best location in spite of the exposed location. The first day was nice and warm but the next morning the temperature dropped and it started with a light rain. By the time I had got back to my car, the rain had started to freeze. So, if nothing else, it proved how much the weather can change in the mountains.
I did get around to actually looking at some Barbour jackets at a saddle shop just down the road from where I work. The are expensive here. All were over $300 and none of them come in a "long," which I am. Filson is about two-thirds of that price, though there are almost no compable garments in the two lines.