Improved LootEntry#getEffectiveWeight - Makes Luck apply a modifier to weight so all loot pools get impact from luck, not just quality. Code licensed MIT - Mojang can use as WTFPL/no restrictions - please pull this into Minecraft Mojang!

LootEntry.java

        // Refactor how Loot bonus applies - 
        // V PCT = Vanilla Percent Chance, M PCT = Modified Percent Chance
        /* base in these tables does not include vanilla quality modifer in this table, but does in code
                BASE    IMPACTED    REDUCED V PCT   M PCT   PCT CHANGE
        ITEM 1  400     12          388     26.67   27.75   1.087
        ITEM 2  100     0           100     6.67    7.15    0.486
        ITEM 3  1000    90          910     66.67   65.09   -1.574
        TOTAL   1500                1398

        LUCK (*10)  100

                BASE    IMPACTED    REDUCED V PCT   M PCT   PCT CHANGE
        ITEM 1  4000    1560        3220    31.74   39.03   7.284
        ITEM 2  100     0           100     0.79    1.21    0.418
        ITEM 3  8500    7140        4930    67.46   59.76   -7.703
        TOTAL   12600               8250

        LUCK (*10)  50
        */
    public int getEffectiveWeight(float luck)
    {
        // This is vanilla
        float qualityModifer = (float) this.getQuality() * luck;
        // Random boost to avoid losing precision in the final int cast on return
        final int weightBoost = 100;
        // This is vanilla * our weight boost
        double baseWeight = (this.getWeight() + qualityModifer) * weightBoost;
        // If we have vanilla 1, bump that down to 0 so nothing is is impacted
        // vanilla 3 = 300, 200 basis = impact 2%
        // =($B2*(($B2-100)/100/100))
        double impacted = baseWeight * ((baseWeight - weightBoost) / weightBoost / 100);
        // =($B$7/100)
        float luckModifier = Math.min(100, luck * 10) / 100;
        // =B2 - (C2 *($B$7/100))
        double reduced = Math.ceil(baseWeight - (impacted * luckModifier));
        return (int) Math.max(0, reduced);
    }

luck 3 30 chests, 7 diamond chest, 1 book (book is rarer)
luck 6, 30 chests, 8 diamonds, no books
luck 6, 30 chests, 4 diamonds, no books
showing good degrees of randomness

Note there are other 'rare' items in the pool that are generating I havent even been counting