This is a super cool idea, I would love some diverse encounters to spice up the fracture sealing proccess and make it more frantic.
The exploiter orb tells her children to get thermia for her in her dialogue in the regular map. Perhaps coolant raknoids could start to show up once the process gets started in order to facilitate these burps.
As for burp ideas:
Tectonica wildlife - much bigger more badass versions of the Valis fauna seeded by the coolant towers' coming back to life they have been corrupted by the reaction between thermia and coolant and emerge howling with blinding rage. They could be designed somewhat like assassins, giving out a howl which prompts dialogue from the business warning which one is coming. Unlike other creatures of the Valis these ones are going to require some subdual before they can be tranqed. Similar to scyto raknoids they could have two-phase fights, one where they deal high damage and a second where they have high damage resistance but can be tranqed. Once put to sleep the business should mention that they will be out for a while and to focus on the fracture or send a number of conservation drones automatically to collect it with a rare resource pop up to indicate that the tag was acquired. I'm picturing blood red stovers with eyes that leave a glowing trail, horasques with scythelike claws and a poison aoe attack, sawgaws that let out a staggering shriek affecting the tenno and corpus alike, bolarolas that curl up and run tenno down like coil drives, verminks that bound around the battlefield like sabretooth tiger sized kavats, fire belching kubrows and pobbers that attack like those leaping moas. In addition to their availability through burps they should probably also be available through conservation during fracture events.
Thermialysts - Buried beneath the valis the thermia has unearthed and evolved a version of the standard battalyst/conculyst variety of sentient fighter. Drop thermia sentient shards which can be consumed for focus like synthetic eidolon shards and thermia sentient cores which can be used for either quills or vox solaris standing.
Thermia servofish swarm - Adapted to the flows of thermia these shoals of servofish emerge and thrash about like walking catfish attacking with their superheated appendages. Fishing spears could work to capture and disable them. Linked shields between the school of servofish could reduce incoming damage based on the number of servofish remaining so a swarm of these flopping menaces could be more formidable when they first emerge and gradually become an annoyance as they are picked off.
A Ravenous Golden Maw - because why not? There seem to be a number of orokin secrets sleeping beneath the Valis' surface. Perhaps they could be defeated by certain tenno and turned against Nef Anyo's reinforcements.
Thermia mushroom infested - a corruption of the Valis fungal spores takes hold over the hapless corpus stationed on venus. A large boil of fungus appears and disgorges infested colored to match the giant mushroom growths of the valis. For a time the Terra reinforcements can become infested with spores and reanimate after death as additional infested. They could have a chance to drop the helminth charger mods.
Additionally, I would like to see diluted thermia be used for kitgun parts and/or even zaw strikes. They could be traded for pax arcanes and/or exodia arcanes to do AOE napalm bursts on headshots or slams.