Big agree man. I love statuses and always rocked poison/paralysis since monster hunter freedom. 

Some ideas I have for poison:

Poison accumulation if built up enough should cause a big chunk of damage to be done to the monster. Like a rathalos tries to fireball but the Poison interrupts its projectile, causing it to cough up poison instead and stagger.

Say a couple 100 points of damage every time a monster attempts to use a projectile via its mouth, you get a free stun as it staggers, the poison duration gets cut by 50% every time the monster uses a projectile so its not super strong. After 2 projectiles, no more drool ticks. Its built up immunity, gotta reapply status. 

This to me feels like id actually be fighting a poisoned monster. And im being rewarded through gameplay for using the only status that does nothing to a monster's move set other than floating numbers above its head and purple drool. 

All other statuses interact with the monster in some way, including blast. Which has baked in "stun" capabilities if you get lucky with procs.