In addition to the vacuous MISD category and the difficulty in classifying vector processors, there are other weaknesses of the Flynn taxonomy. In the MIMD category, all arrays of processors are lumped together regardless of how they are connected and how they view memory. Since these characteristics can have a dramatic effect on performance, it would be desirable if the taxonomy reflected those differences.
Shore (@Shore) offered a very similar taxonomy, but expanded the SIMD category to four subcategories. He still did not distinguish the pipelined vector computer and he also did not provide for the completely independent array in the MIMD category.