Soulframe isn't a Soulslike, but that doesn't mean we can't have poison swamps! Ichor doesn't seem very safe to trudge around in, spending time wading through/soaked in it should build up into a debuff for our Envoys.
Since actual poison would be quite punishing (and a little cliché) I'd make it increase the cooldown on Arcanics.
In Cogah mode the effect could be made harsher by blocking Arcanic casting completely, similar to the mechanic used in the Wazzard fight. As the debuff builds it would lock Arcanics one at a time, Smiting an enemy (or simply staying out of Ichor for a while) could clear the debuff