I think that the long exhaust snaking up the side of a bike not designed to have an undertail exhaust tends to look kind of cheap and crappy. It can be done and look good, but it takes a lot more care and design than just running the pipes up to an underseat muffler.
If you switch to mono and run a 4-into-2, you can have a nice looking balance on both sides and have the room to tuck an exhaust pipe fairly tight in each side to run it up under the seat. With the dual shock setup, I think it's going to be harder to find a workable solution, but maybe you can figure something out.
I really think that the key is to run the exhaust as tight as possible to the motor, and then inside the frame. This isn't an I4 bike, but maybe it gives you some ideas:
The mesh tail could look good, but you'll want mesh elsewhere on the bike to tie it in, otherwise it will tend to look unbalanced/unfinished. What about a mesh flyscreen up front? Or mesh sidecovers? Or mesh trim in the front fender and a mesh-trimmed rear hugger?
If you do go for a mesh tail and underseat exhaust, take care to use a muffler or mufflers that look GOOD! You could pick up a stock 999 muffler pretty cheap and it might work for you - I used to hate the looks of those but they've grown on me. It's compact and was designed to hang out the back of a bike. It even has mounts for turn signals, brake lights, and a lic plate. Actually, I might wanna do this myself.
It could be a neat/different update to the old classic 916 tail/mufflers on streetfightered GSX-R's.
