@ikrase I think so as well, but I would like some quantitative figures

I guess the text to the orginal question was not clear enough, so I modified it now.

In the original question I sketched some power source (thin foil phtovoltaics) which can achieve such power density. Other possibilities may be high temperature nuclear reactors with magnetohydrodynamic or thermoelectric generators. It is not of-the-shelf thechnology, but it does not require any theoretical breakthrough to develop. As I explain in original question, the possibility to construct such power source is the very motivation why to thing about possible boundaries to minimize mass of ion engine.

Amtzi - I explainded why I think mass of solar panels could be reduced so much that bottleneck start to be elsewhere

or put it in reverse - I know about some technical solutions how to reduce mass of power-generation by orders of magnitude. Now I wan't to know where is the catch / challenge doing the same for thruster itself.

Russell Borogove > there are several engineering solutions how to deploy large solar panel in space and keep them aloft. My favourite is to use purely tensional structure inflated by centrifugal force (the same way as some solar-sails). But I don't want to discuss particular realization, I'm interested in fundamental limits and figures of merit.