I had been searching for a similar WP and LW outer shell for 4 months. I tried the OR Versaliner gloves as the WP shells only weighed 0.8 oz. While the fabric was WP the seams were not and my hand got wet right away around the all seams by the fingers. Trying to seal a glove looked to be about impossible due to all the seams in the finger area.
Terra Nova makes a few options as well. In the Extremities series, you have the Tuff Bags and the Top Bags. These are both mitts. The Top Bags are much lighter at 1.3 oz per pair, however Terra Nova does not recommend you use them with trekking poles as I believe the fabric is not strong enough for this. Instead, the recommend their Tuff Bags. The Tuff bags are a Gore-Tex material and weigh about 2.5 oz / pair. The Top Bags are not Gore-Tex rather a in-house 100% nylon fabric they say is WP and breathable. It seems like there is a debate on how well Gore-Tex breathes. I have not really liked it myself, yet have very limited experience and it was years ago. Terra Nova also make a WP running shell called the Ultra Glo that is made from Cuben Fiber that weighs next to nothing, yet, it is not seamed sealed either so not 100% WP.
I had the MLD eVent mitts before and they were fine, although, I never sealed them so obviously they were not WP. At the time, I was doing some serious boulder hopping in the Wind River Range each year and I was afraid they would torn to pieces so I sold them. I have talked with other who have stated that seam sealing the MLD shell or any glove / mitten shell is a real pain. Over time the sealant starts to fall off and sometimes they are not 100% WP either. I also know some people say their MLD gloves are WP so maybe it has to do with the technique when sealing, etc. I have not tried the Zpack gloves yet, however, I had a friend who has them and said the thumb was a bit small when he used them with his trekking poles. I believe he wears an XL size so if going that route, I would encourage you so talk to Zpacks and see if Matt could make the thumb made a bit bigger if you use poles often.
You might also want to check out the Mountain Hardware Epic glove. This is a fully WP option that is also a glove. It might not be UL at 3.1 oz /pair and maybe not as good for keeping the hands warm as a mitt, however it gets really good review for being 100% WP right out of the box. I am looking to get the dexterity of a WP glove over a WP mitt as keeping my hands warm is usually not a problem based on where and when I hike as long as my hands stay dry. Seeing they are only a few oz more than the Tuff Bags and offer the glove benefit, I am leaning towards them unless, I can find anything better. If I was going after a mitt, I would probably try to get the Zpacks mitt with a bigger thumb and go that route. I don't know how they would last, yet, like most of the SUL items, it might be how we treat them. Obviously, everything is a trade off.
Hope this helps and good luck in your search.