The biggest disadvantage to the kayak as a fishing platform in this situation is the difficulty in spotting fish from a seated position close to the water. The carp fly fishing game is all about sight fishing, and being higher off the water (even if seated on a cooler and not standing) would be a big advantage.
The next advantage to the SUP option vs. my current kayak would be transportation ease. At 13.5' long and 70+ pounds, my fishing kayak was not the easiest thing to throw on top of my Jeep. I resorted, at times, to using a hitch extender and sticking the kayak out the back of the Jeep, and even though it was well-secured, it never felt truly safe or "right" to me. Going along with the transport advantage of a shorter (and lighter) SUP would be maneuverability in smaller water. Some feeder creeks and smaller streams where I had used my kayak, I barely had enough space to turn it around in the water. The more I thought about it, the more it made sense to me to try a SUP as a fishing platform.
Prior to going on vacation last week, I ordered a Kaku Kahuna (http://kakukayak.com/) 12' SUP from Austin Kayak (http://www.austinkayak.com/). I got a great deal on the board, and free shipping was the icing on the cake. Due to being out of town for a week, I had it shipped to a family member, and brought it home earlier this week. I was never so happy to see an ugly box!
Since the board was packaged, and I didn't have my roof rack on the Jeep (plus I was in a hurry), I used the bed extender to get the SUP home.
The Kahuna comes in at 12' long and 60lbs, 34" wide at the widest point for stability. Although it is not substantially lighter than my kayak, it feels less bulky and easier to carry/lift than my kayak ever felt. The 12' length also allows me to store the board inside, whereas I never had room to keep my kayak out of the weather. I have small plans to add a cooler (both as a seat and storage) and to build my own push/stake out pole for carpin' the mud flats. The one thing I am yet to figure out completely is where/how to mount a static video camera for filming. I plan to continue using a wearable action camera, but like to have a static mount camera to get a second filming angle, as well.
Our recent cold snap in SE Ohio has put hard water back in play, but as soon as we have thawed and I have the board rigged, I can't wait to get out on the water. I truly believe this will be the perfect watercraft for sight fishing carp with fly gear, as well as exploring some small streams for bass close to home that are difficult to wade or fish from the bank. I expect big things from the Kahuna this year!