I like the idea but some comments:

-the section a-a location with biggest drop to the coaming is most likely at the deck peaks which are at the front or back. Some deck configurations would put this at the 10 or 2 o’oclock configuration(ww yaks). As most boats have rounded decks the low pt would then be to the side where you’re a-a is located. As this is a low point it is a fairly good idea to exploit it and use this location (or a few inches to rear) for drainage – either a ‘canal’ or design the recess so it is at 0 at this location.

-If your yak is normal or narrowish and you wish a full size cockpit, maybe getting rid of the ply stacks for coaming upstand will give you 1 ½ “ of extra space. To me they are a bs approach that just adds weight, adds wider coaming ring and takes away possible usable width, and with real curvy decks adds difficulty in actually bldg.

-Carefully consider drainage and the conditions that this yak will ever be in even without you. I have frequently had ice forming on my skirt - a non-drained recess would inadvertently make me ‘one with the yak’, maybe at a time that I may not wish it. In one yak, I put in a continuous recess as I didn’t want to aesthetically interrupt the strip continuity, but then installed 2 scuppers – a marginal solution. In the present yak, I’m planning on putting ditches out on ea side. in narrow yaks, there's little to no room for a recess at the side

-mick