Hi Arne - yes, your terminology "slingpoint" is correct and mine was wrong, I have gone back and changed it.
Also you are right, the yard slingpoint will probably be about the middle of the yard on Amiina Mk2, with, of course, allowance for fine tuning of the slingpoint position which will be expected, in practice.
Mast/Halyard angle: My concern was, and I did use the wrong words - the point at the mast where the halyard begins. That's the point which needed to be shifted up a bit, to get the smallest possible angle between the halyard and the mast. I don't know what that angle should be, and I think you know better than me about that, but I did find by trial and error that the masthead point where the halyard starts has to be at least as high as the peak of the yard, and higher is better. It wouldn't surprise me to find that this rule of thumb applies to all low yard-angle rigs, but I only know about the Amiina Mk2. The higher the halyard crane, the lower the mast/halyard angle, and as you know, its that angle which is ultimately what gives that undesirable forward-seeking component of the halyard force on the rig, when it is fully hoisted. To me, your drawing looks better now. I am just documenting it, I realise that Arne knows all this.
Forward rake of mast: For people with forward sloping masts, that critical angle we are talking about is the angle between the halyard and the vertical, actually (not the angle between the halyard and a forward leaning mast). A forward leaning mast exacerbates the halyard angle problem, and although it is a desirable and endearing feature, I don't think it suits SJR unless one is willing to dispense with Slieve's parrel system and revert to a suite of conventional parrels - of which I have virtually no knowledge so can't comment other than to say it is then no longer a McGalliard SJR, it is something else, (hopefully, even better).
You can count that as a disadvantage of the McGalliard SJR if you like, if you tend to sail in rolly-polly conditions when the bundle won't lie quietly in a calm or near calm. Annie explained to me one day, that if the mast slopes forward, the rig will swing out to leeward and tend to stay there quietly rather than slamming back to central all the time which will happen with an aft-leaning mast - this happens even with a bermudan rig and a vertical mast, but with all the weight of a Chinese rig with all its battens its more of a consideration. I guess those old Chinese shipwrights knew a thing or two about the junk rig.
For Marcus: No rig gives you every advantage and you go crazy trying to tick all the boxes. With SJR you don't have the luxury of a forward raking mast, and thats just something you have to forgo unless you want to dispense with one of the advantages of SJR which is the potential for minimal horizontal forces on the rig and the ability to use only the McGalliard system for holding the sail to the mast. Its a trade-off. I wouldn't want to over-sell the "less parrel stuff" advantage - most people seem perfectly happy with conventional rigs and for me its not a big deal, just my own personal preference. I wish I could have my cake and eat it too - I have come to just adore the look of a forward rake.
Anolther disadvantage of the SJR, which is closely related - or, should I say, another potential feature which the SJR does not have, is the ability to adjust the drape of the sail fore or aft while you are sailing, to get the balance just right and take a bit of load off the helm. With SJR once the mast is in place you are stuck with what you've got. You can't rake the mast forward, or back to vertical, to make a permanent improvement to helm balance, and you can't sling the sail forward or backwards on the mast to make a temporary adjustment to helm balance. People with contiguous rigs do have that liittle advantage if they want to mess around a bit with hauling parrels, which you won't have with SJR. Some people have favourite positions for the sail, depending on whether on the wind or off the wind. SJR can't do that. I just point that out to explain why there is no "BEST" rig, they all have their good points and a lot of it is just personal preference - especially if high performance is not your priority, as David explained to you.
For Arne I wonder how the hybrid HM/SJR will drape. I note the advantage of your higher yard angle (more sail area or shorter mast, depending on how you look at it) but there is more to getting the sail to set nicely where you want it than just the mast/halyard angle. Would you expect to use Slieve's system of spanned running batten parel downhauls - or would you expect to use the conventional parrels as per your Johanna rig, to hold the sail in the position you want? I'm sure one system is as good as the other, but I would hate to have to use a hybrid combination of both. Whatever, I think the SJR panels are each going to need a light downhaul, just to keep the jib and main luffs more or less straight, so I am waiting with interest to see what you have in mind here.
For David ditto, same question as posed to Arne, and even more so with your shortish forward raking mast on your proposed Poppy-Siblim hybrid. No-one has answered this question yet.
Your excellent points about "planform" are only from the point of view of the sail-maker, important though that may be. If we are seeking better performance, are there not aerodynamc matters which also need to be optimised? Also I think you have glossed a little too quickly over the issues facing a first-time sailmaker. One of the most important values of the junk rig is that it is open to DIY and long may it remain so. Starting off with something smaller is always better for the beginner, if there is the opportunity. But is 50 sq m really too big for a first time sailmaker? Aren't there a few counter examples out there? If it is better for the beginner to start with something smaller, it is equally important to start with something simpler, so this would seem to be an argument against the Poppy rig and a response to your question "what's not to like?"
As for Poppy's sail being easy on the eye - well, I 100% agree, in fact I think that is an understatement. This is one of the more iconic and beautiful photographs in the entire JRA gallery. It's not one of those perfectly cut sails you see in the yachting magazines from time to time, but in my opinion it is absolutely stunning. Evey panel bulging and the sail pulling like a team of horses. The word which comes to mind is "windjammer".
For right reasons or wrong, I bet this photo has created more interest in SJR than all the technical discuissions put together.
It would be an absolute delight to see that sail on SibLim.