Ok so the way I see @Thorgors change working is as follows.
Any Toxin and Gas weapon gets a fixed Str of 4 on its profile.
The Toxin trait just keeps to wording about instead of applying damage it just results in the rolling of 1 injury dice per unsaved toxin 'wound'.
The Gas trait keeps the above as well as its ignoring saves wording (this might need some clarification on exactly what 'saves' it ignores based on the discussion we've had round saves in other threads).
The following wargear/traits/abilities can keep its wording as is (or be slightly modified but functionally its the esentially same).
Chemsynth: targets toughness is reduced by one, this works with the new toxin str 4 as above, in most cases it results in the same effective number needed to inflict a wound on the dice as previous)
Respirators: increases targets toughness by 2 vs gas, effectively works still, slightly less effective for a T4 fighter being boosted to effective T6.
Filter Plugs, as above.
Esher Chem Alchemy Traits
Acidic, nullified respirators and the like, so works still
Bane, target is treated as if their T3 regardless of their actually toughness characteristic, so works still.
Hallucinogen, needs rewording to say ... in addition to the to wound roll, rather than in addition to the toughness check.
Concentrated: Works, but change language to 'add +2 to the to wound roll' instead of it's current wording.
Puke: Works as is but language should refer to the to wound roll not 'when testing', slightly less effective for a T3 fighter than before.
House of Chains Genesmithing:
Hardened Immune system, works as intended. Just needs to refer to only ever wounded on a 6 not 'affected'.
Adaptive Biology: Need changed, but obvious is forces successful wounds from Toxin or Gas weapons to be re rolled.
Industrial Respirator, works as intended vs Gas.
Hazard suits, works as intended vs Gas.
I think that's all the items and rules than interact with the toxin 'toughness test' and how they might need reworded if we move to the Str4 idea.
Functionally the only of note change that this obvious 'read across approach' does is that filter plug and respirators (unless combined with a hazard suit) are functionally pointless for T5 models (it doesnt result in a lower to wound roll vs them), it does help them a bit if the toxin or gas hitting them is affected by a chemsynth.
As I said, if the project decides this is the way I'm ok with that but I'd be happy keeping toxin as it is.
Hope this is at least helpful.