No "global modal system"
Hypothesis examined: three sets of particles (the conditionals, the affirmed or negated future, and the pair كي / لعل) would form a single system graded by certainty. The grouping adds nothing to what is already established, and two of its three pieces do not hold.
The first piece, the three conditionals, is sound; it has its own fiche (“When, if, if only: the three conditions”).
The second piece, the pair سوف / لن, is rejected: neither symmetry nor any verified preference.
The third piece, كي / لعل, is not a gradation. The particle كي gives the purpose of an act: "so that it does not circulate among the wealthy among you" (59:7). The particle لعل expresses an open expectation, which the translation renders "perhaps": "perhaps you will guard yourselves" (2:21). These are not two degrees of one purpose, but two different things.
A synthesis whose pieces fall cannot be a rule.
In the text
كَىْ لَا يَكُونَ دُولَةًۢلَعَلَّكُمْ تَتَّقُونَ