Arne, congratulations on persevering with the dinghy design. I think your little vessel is a thing of beauty, and I anticipate that your rig might prove to be a landmark innovation in junk rig development for small craft.
I have some criticism though.
The hull shape is a little more sophisticated than I think is warranted for such a small boat, though the way you have developed the panels, you will have eliminated much of the difficulty for a builder, so maybe it will not be too difficult to build one. Its key feature and virtue is that midship section and the way it responds to increase in weight.
My main criticism is the bow board. No-one else has so far commented on this - maybe it is "the elephant in the room"? This bow board seems to me to be innovation for innovation's sake. I am sure it will work - but why? Perhaps I am striking too soon, before seeing the detail of how it is to be mounted and deployed.
Perhaps in the "half up" position (if it has one) it would give an increase in the waterline length? It seems to me that this bow board will be practical in only a very limited type of coastline - and considering that almost all dinghy tenders (outside of marina use) will need to take shelving beaches or shallow water for most of their working lives, I would like to suggest that you make an alternative conventional version available as part of your design package.
Another thing, I can't see the bow board contributing much to directional stability, to put it mildly. It will need to be pretty accurately and firmly mounted, or it will take charge. (My old scow had a board which was floppy in its case, and when motoring or not hard on the wind, every time it flip-flopped the boat would want to take a sheer in a different direction - needed constant attention at the helm!)
If reverting to oars, I imagine it will need to be fully up. It will probably have too much windage to have an "up position" and I can not see it being especially easy to reach forward over the bow to retrieve it (and then have to stow it somewhere).
Perhaps if it were mounted inside the bow, the case could be an internal part of the structure of the forward buoyancy tank, so that the board can swing up and remain out of the way - or, if a dagger, be accessible from the sitting position inside the dinghy, to be pulled up a bit, quickly, when (not if) it strikes the mud or sand.
I am not qualified to comment on leeboards and their variants, never having used one, but can't help wondering if this dinghy, with its conveniently vertical topsides, is asking for a "clip on" external swinging off-centreboard, which can be left in place, or removed at will. (I mean fore-and-aft swinging, not the conventional "broken wing" swing-out of the true leeboard.)
I think the "sausage fender" is very well suited to a dinghy which is narrow in the beam, or a little tender (the adjective). However, on this beamy little boat it might not be quite so necessary and will not add anything to its looks. Good safety compromise though, for a sailing dinghy which does not have built-in side buoyancy.
Of course, the client must have the last say on all these matters. As for myself - I take my hat off and thank you for for putting forward such a courageous, imaginative and delightful creation. I am looking forward to the next iteration.
PS Also hoping David will progress his thinking, at least to the "proposal" stage. Much as I like the "pre lim" - it would be good to have a "san ban" also for consideration, as I still think "three planks" is good enough for such a small dinghy.
pps another afterthought: a side-mounted board would perhaps have to be too far aft and not suit the rig. The more I think about it, if the reason for the bow board is to keep this appendage out of the dinghy and out of the way, a centreboard case right in the bow, while complicating the structure a little, would make sense to me, especially if the board can swing up into it without needing attention. There is a buoyancy tank there anyway, so not much internal space is lost if the board and its case are cleverly shaped, the case fitting into the tank and under that forward thwart. The little bow board could stay permanently in its case, and just swing out when sailing, the rest of the time out of sight and out of mind. I don't think it needs to be so deep either. Well, that's just my opinion