MCU Phase 4: 10 Things They Must Address (And Not Just Forget About)
9. Pym Particles
Hank Pym is a smart cookie, so much so his crowning scientific achievement is still sought after by villain and hero alike. The Pym Particles remain a hot topic within the MCU due to their capabilities for changing the mass of matter, and also for Quantum Realm tomfoolery. This was a plot point in both Ant-Man movies, so it stands to reason they'd still be a powerful possession.
There still remains the character of Ghost, who needs quantum particles to survive, and Walton Goggins' character who was hell bent on acquiring some particles of Pym for himself. Either one could return as an antagonist in the future, either for Ant-Man again or another hero.
On that note, there is still the matter of tensions between Hank and the Avengers considering his first appearance in the MCU was in conflict with SHIELD about the particles. They're such a useful thing to have, so it's reasonable to imagine SHIELD and the Avengers would have at least a few uses for them.
The MCU moving forward needs to remember the Pym Particles, and not just their scientific uses, but the conflict that comes with them, both against villains and heroes in the universe.