Thanks for the responses.
My marquetry skills are pretty rusty, so I'm leaning toward an inspection port with a ditty bag insert in the rear bulkhead.
But John raises another point of consideration.
I've had a wooden back rest in mind, paired with a nice cushy foam seat (I'm looking at the "Happy Bottom" seat. The integrated thigh braces seem like a nice touch given the roomy cockpit.).
A lot of backrests attach to the seat below or the coaming or cheek plates to the fore- I'm thinking of attaching it to the deck from behind. Here's a simple rendering:

Two curved laminations attach to the back rest and bolt to the deck for simple removal or re-positioning.

However, I'm concerned that this could be a bad idea- the backrest, and thus the deck- could see a lot of downward pressure when entering the kayak. While I like the idea of a clean, "floating" backrest, maybe the reason I haven't seen this elsewhere is because it's a lousy idea...

Any thoughts on this approach or similar alternatives?

Thanks,
Patrick