Don’t call me an expert here, not by any means, but my impression as to why your maple syrup failed is insufficient acidity. Pectin gelling is the result of a sugar-acid interaction, thus either too little sugar or too weak acidity is problematic. Maple syrup isn’t acid, and thus wouldn’t gel, I don’t think. You’d need to add something acidic in order to get it to do so, and this in turn would affect the flavour at least to some degree. You might try adding calcium ascorbate, a form of vitamin C with a relatively mild flavour. A side benefit is that it should help to enhance shelf life a bit.
I think a more productive line with maple syrup, anyway, wouldn’t be a jelly but something like maple butter (not maple syrup mixed with butter, but rather maple condensed into a butter-like consistency, rather like set honey – being in Canada I suspect you’re familiar with it). Another idea is a maple syrup from Shady Maple Farms called “Clearly Maple”. It’s got at least twice the thickness of even ordinary thick maple syrup (spoonable, like heavy corn syrup) and a better, more robust maple flavour. I recommend it highly in any case as simply the best maple syrup one can get (at least IMHO).
Back to pectin: If you recognise the fact that it’s sugar/acid based, it’s easy to see why fruits such as raspberries (with good acid and sugar content) tend to work whereas other things, either insufficiently sugary or insufficiently acid (I think this is what plagued your lychee experiment – again, not enough acid) don’t, and this will help you to make intelligent choices about what jellies to offer.
Another thickener you can use, btw, useful for “jellies” with low acidity, is tapioca. If I think about it, this might be a good way to go with maple syrup (the tapioca has a very neutral flavour). You add enough water to the tapioca to get a good jellylike mix, then pour in your syrup. Just a thought.