The change to Hextech makes it a stronger AP item that happens to synergize with the AA-centric portions of her kit (E and Q) by offering a little bit of AD and some lifesteal. As such, I can see it being a pretty solid item for AP Tristana.
But... well, looking at the build you recommend (Assuming you intended Hextech as well as your list:
), you're looking at the following stats:
150 AD, 260 AP, 20% Lifesteal, +75% AS, 40% CDR, 40% Spellvamp, plus a handful of interesting passives and actives, but with no penetration.
Alternatively, a pure ADC build (
), would have:
200 AD, 20% Lifesteal, +75% AS, 55% crit, 35% Arpen, 50 Armor, 50 MR, plus a handful of interesting passives and actives. The added benefit of armor pen and defenses offered by the focused build means more survivability and more effective damage to tanks and bruisers.
A pure APC build (
), would have:
598 AP (including Rabcap passive), 20% cdr, +100% mana regen, 35% Mpen, 15 flat Mpen, 50 Armor, 50 MR, plus a handful of interesting passives and actives (including replacing the Grievous Wounds lost from her E). Again, the additional benefit of Magic pen and defenses means more survivability and more effective damage.
I stand by what I said: Pure AD or Pure AP is almost certainly more effective than hybrid. Which is not to say that hybrid doesn't have a place as a niche build. But I don't expect to see it suddenly become the Trist build.