Have minor line experience here, but some thoughts.

You want fittings as recessed as possible as when you clamber up in dire conditions, anything anything anything that grabs onto you pfd, drysuit, booties or hacks your hands is problematical. Esp up near the rear of the cockpit where you will be scrabbling around for sure. I've had enough jabs in the rear and I can just feel the wetsuit ripping!

You want lines that are as tight strong and paddle stabilizing as possible and yet quick to put the paddle under. So for initial(as soon as you put it in)tightness use bungee line. For strength use 5/16 or larger to good backed fittings. For stabilization use lines as far apart as possible with alternates in between for screw ups. Many yaks have the X but my reactionis that its too easy to screw up, so my first try would be like your W but doubled like lUUl where the spaces between the letters are zero. Like 6 fittings, 2 on ea edge and 2 down the c/l. The base of the UU's is against the cockpit so the lines are aesthetically placed to follow the cockpit and also the loops are easy at hand to pull or yank. Diagonal lines just cause problems when using and more importantly, locations for the day hatch aren't compromised by diagonal lines going over. You can place a hatch on either side, just make it(them) flush so no compromising ease of pushing the paddle thru or holding in place or dislodging when paddle racking back and forth.

For ease of use, I'd fix little rubber szuare cut cylinders or tubes(preferred) or balls in the c/l of each line and underlap to allow the paddle to easily slide under the lines.Like they're slightly separated from the hull. But at the outside lines, what about putting 2 small ones side by side about 1 in apart to that the paddle shaft (no matter which side used) is more likely trapped in the groove betw the cylinders.

And if we're dealing w/ safety, every pc of line at every fitting here should be tied off or say double knotted at each side of the fitting. NO continuous line b/c why have multi fk ups if one pc breaks????or the whole assembly goes? Especially when it counts. So redundancy. One breaks - 5 more to go.

I really like the idea of (recessed of course) jam cleats every where, but don't know how you'd release them. So maybe just 2 as you infer on the outer first fitting only (1 is fixed) so there is some possibility to fix. this is the line for the double cylinders (maybe make them sliding on the other line as well)

I'm also intrigued by the idea of the free end having a loop and being a step-cinch. It's a step up into the yak but also cinches down the paddle by doing. Could maybe stay in that position for a while, while resting.

anyway some thoughts - haven't tried these

-mick