The 86kg value (previously 90kg) in Section S used for W&CG requirements is still there for weight requirements, but there's been a partial de-coupling.
So, a microlight must have an empty weight not greater than MAUW - 86kg/seat - 1hrs fuel at maximum continuous power. This is identical to the requirement in CS.VLA for non-aerobatic light aeroplanes.
However, whilst it was originally coupled also to the CG and structural requirements, that's been de-coupled in recent years out of necessity. So, It's now possible to use any higher (than 86kg) weight the designer selects so long as at the permitted seat / fuel loadings the aircraft remains within CG limits, and the structural requirements are met for the seat/harness/surrounding-structure at those higher seat limits.
If you look at CS.23 or FAR-23 (or part 25), they are subtly different in that the empty weight issue is still there (albeit using slightly different numbers, typically 77kg/seat and 30 minutes fuel), but there is no CG issue - it's assumed that the pilots of part 23 aeroplanes are capable of doing W&CG calcs (whether this is true or not is a moot point, but they've been trained to
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