Patrick,
Great essay! completely fundamental and original, and also well structured, explained and illustrated.
I completely agree the external observers viewpoint. (I've analogised this in my own work as very similar to the two views of our galaxy -my last two essays, end notes and links refer).
The expanding spheres are analogous to Huygens construction. I like and agree the concept and have also used it, viewed it in a slightly different way, discussed in my essay.
But I was most interested in your explanation that;
"An internal observer on the present layer will always be at the centre of his own virtual 3D world. That world is constantly growing around him. ..., the successive virtual 3D worlds are like Russian dolls, they envelope one another."
This hierarchical 'space within a space within a space' model is something I've explored in my last 3 essays, finding an ontological 'discrete field' model (DFM) which proves to contain high empirical truth value. I test some important implications in my essay which I hope you'll read and comment on. Many of your points have analogies.
I also agree with most of your conclusions but not entirely with some. My own most bold proposition is that the 'Law of the excluded middle' applicable to maths needs modification to account for the uncertainty of nature! Perhaps best to discuss 'hidden likenesses' once you've also read mine.
A very good essay, using very free thinking and making an enjoyable read. Thank you. Certainly worth a better score I think, which I'll apply now. I note you felt you "crammed too much in", you just wait till you read mine!! I hope I did it as well as you, ...but perhaps don't try to 'speed read' it!
Very well done and best of luck in the impending melee
Peter