Is there an ideal lift distribution for human-powered aircraft?
The essential feature of a human-powered aircraft is to maximise aerodynamic efficiency, which is to say to minimise drag for a given amount of lift. This is what the bell curve achieves. The elliptical distribution minimises drag for a given span, which says nothing about the lift available. The bell curve also gives you a lighter structure for a given amount of lift. Yes you can brace an elliptical wing for reduced weight, but you can brace a bell wing for an even greater reduction.
Also, the ideal distribution will depend on things like how tightly you want to turn. The inner wing will tend to stall, the outer wing to drag backwards (adverse yaw). Jonathan Bowers at NASA has shown that achieving the bell distribution through significant washout can create negative tip drag and proverse yaw. UK pioneer JW Dunne published as much in 1913. Washout also greatly reduces the problems of tip stalling and Dunne's biplanes proved wholly unstallable.
No doubt computer simulations could help refine the exact optimisation of washout, airfoil variation and span loading for the flight regime envisaged, as they did for Bowers' PRANDTL-D research drones, but it is not going to be far from the classic bell distribution.