This article explores an emerging frontier in optical communications - leveraging optical computing and optical signal processing to restore degraded signals in spatial or mode-division multiplexed (SDM/MDM) systems. As SDM/MDM pushes toward ever-higher channel densities within a single fiber, inter-channel optical coupling leads to significant crosstalk. Due to group velocity mismatches, this crosstalk spatiotemporally entangles optical signal streams, significantly complicating multi-input multi-output digital signal processing (MIMO DSP) for signal recovery across both spatial and temporal domains. Free-space optical systems face similar challenges from multipath interference. This article systematically appraises two strategic pathways of optically addressing the spatiotemporal interference: (1) optoelectronic computing that either accelerates conventional linear MIMO DSP or maps the problem onto physics-inspired models solvable by analog or hybrid optoelectronic systems; and (2) all-optical processing that seeks to untangle the coupled optical signals directly within the optical domain. For both pathways, the article evaluates architectural effectiveness and scalability based on rigorous mathematical analysis, aiming to offer insights into promising approaches for future research.