If semi-spaces are tethered to, say, a mount's saddlebags, and there were people standing upright in the semi-spaces so that their upper bodies were sticking out, would the weight affect the mount? Would the people sticking out of the semi-spaces affect the bulk of a cart they are tethered to? What about semi-space armor?
Speaking of Yggdratectural exploits, what about semi-space armor? It wouldn't weigh anything at all, projectiles would usually end up in the semi-spaces, and it would provide virtual immunity to melee attacks.
Also, are semi-space portals transparent from behind? If they are, a character could be completely covered in semi-spaces and be nigh invulnerable.