The HP/1000 was considered like a 16-bit "expansion" of the 12-bit DEC PDP-8. Its addressing mode for loads and stores similarly used pages, base page and current page, and allowed for indirection.
However, during indirect load or store, the HP/1000 used only 15-bits of the memory word as pointer to address memory, reserving the high bit in the loaded pointer to request an additional indirection: as long as the loaded pointers had their high bit set the HP/1000 would continue indirection for that instruction.
One architectural cost for this feature was 1 bit of address space, so given this feature, the computer could only access 215 words instead of 216 words — effectively halving the potential address space. This extra capacity and much more was in demand for many applications, and, like the PDP-8, they had to use alternative mechanisms to address larger capacities (they would have had to do this anyway, but an additional 32k of directly addressable words would have been put to good use).
I'm interested in any code sequences that would have motivated architecting or would have benefited from using the multiple/repeating indirection feature. (I did compiler work for the HP/1000 and never used that feature!)