SYSML14 — QUDV's Unit::quantityKind and Unit::primaryQuantityKind are redundant and too limiting for reuse across systems of unit

SysML issue 18692 raised the problem of reuse of definitions of Units and QuantityKinds across SystemOfUnit and SystemOfQuantities respectively.
For example, the SI SystemOfUnits has 7 base units: meter, kilogram, second, ampere, kelvin, mole and candela.
These base units are in 1-1 correspondence with base quantity kinds in the ISQ: length, mass, time, electric current, thermodynamic temperature, amount of substance and luminous intensity. (See SysML 1.3, Figure D.5).

The association between Unit and QuantityKind where a QuantityKind is the Unit::primaryQuantityKind for a given Unit is redundant with the choice of SystemOfUnits::baseUnit and SystemOfQuantities::baseQuantityKind.
For example, in the context of the SI, length as a baseQuantityKind of the ISQ is the "primary quantity kind" for metre as a baseUnit in the SI.
Conversely, length as a baseQuantityKind of the ISQ is not the "primary quantity kind" for kilometre in the SI because kilometre is not a baseUnit of the SI.

From a reuse perspective, it should be possible to define a coherent, non-SI SystemOfUnit whose baseUnits are the same as those of the SI except for replacing metre with kilometre.
This non-SI SystemOfUnit would be coherent with respect to the ISQ because length, as a baseQuantityKind of the ISQ would still be the "primary quantity kind" for kilometre as a baseUnit of this non-SI SytemOfUnit.
To support this flexibility of reuse of Unit and QuantityKind definitions, it is necessary to eliminate the Unit::primaryQuantityKind association from QUDV and instead derive the "primary quantity kind" of a given Unit in the context of a particular SystemOfUnit.

Furthermore, such a non-SI SystemOfUnit could define "inch" as a QUDV::LinearConversionUnit by reference to metre. In SysML 1.3 QUDV, this would require "inch" to specify that its Unit::quantityKinds are length.
This is redundant with the fact that metre already specifies length as its Unit::quantityKinds.
This redundancy could lead to inconsistencies if users define derived units and forget to specify their Unit::quantityKind or do so differently than the Unit::quantityKind of their referenced unit.
The only kind of Unit where it is logically necessary to specify Unit::quantityKind is for QUDV::SimpleUnit. In all other cases, the Unit::quantityKind collection can be derived.
For example, for any kind of ConversionBasedUnit, it can be derived by following ConversionBasedUnit::referenceUnit and querying that Unit for its quantityKind collection.
For a DerivedUnit, it can be derived by following DerivedUnit::factor and UnitFactor::unit and querying the Units for their quantityKind collections.

see pages 255 - 258 of ptc/2013-12-08 for details