I can't say I see the need. We have Recon chassis for all-terrain and jump seems better designed. A spider comm could constantly peek up cliffs or hide in holes, whereas Recon has to commit to a jump. Existing maps also take Recon into account, whereas a spider chassis would have trouble dealing with particular types of cliffs with moats.
All that said, it merely seems difficult to balance, not impossible. It seems distinctive enough to have a spot in the roster and it would be neat to see what sort of tricks it could do. So I think it would be added if someone modelled one (solving the aesthetic problem raised by
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skuggmodzer0) and did a bit of design.