In recent years, the commercial impact of optical data storage systems has been displaced by new technologies. Historically, optical data storage displaced older technologies, like consumer magnetic tape, so it is not unexpected that the same fate could pass optical data storage technology into the "retro" domain. In this paper, the basic building blocks of optical data storage are discussed, and limits based on current understanding are presented. Then, conceptual and philosophical arguments are presented to direct intuition toward future possibilities that may provide avenues to develop displacement data storage technology. For example, current understanding puts minimum practical data mark transverse dimensions in the range of 10nm by 10nm, regardless of recording technology. At the conservative assignment of 1 bit per mark area, this mark size equates to about 6,500 Gb/in2 (109 bits per square inch) of surface area. In order to gain the attention of research investment, displacement technologies need to target a 100X improvement in data density or about 1nm by 1nm mark size, with an effective surface data density of over 650,000 Gb/in2. Research and engineering mindsets for displacement data storage technologies should address this goal to be considered significant. Otherwise, advancements in known technologies will probably evolve to satisfy demand.