A common complaint in the current PvT meta is that Terran relies heavily on allins to avoid facing Protoss in the lategame. Ever since 4.0, two-base allins have been popular or even standard for Terrans in the matchup at the pro level. The new Colossus was cited by the Unity teamhouse pros as being a key factor, and they suggested a revert to the pre-4.0 version. Others point at the new chrono, the new recall, or any number of 4.0-era changes. Ravens have recently received a great deal of attention, but games that reach the super-lategame of Skytoss vs Ravens are rare at best. In any case, it should be clear that heavy reliance on allins makes for an unhealthy meta.
Of course, Protoss has problems of its own, specifically in the PvZ matchup. Directly nerfing Protoss is thus a suboptimal approach. Conversely, TvZ is widely considered to be in a healthy state at the moment, so giving direct buffs to Terran is equally poor approach.
In this context, a change that improves Terran lategame against Protoss without affecting Zerg would seem to be the magic bullet. Enter Snipe, a tool widely used against Zerg but never Protoss. Removing the restriction on biological units only would obviously have zero effect on TvZ, while (hopefully) giving Terran a new tool against Protoss.
It’s not a perfect solution by any means, but it is a narrow change with minimal impact on other matchups. If nothing else, I hope it’s a step in the right direction.
EDIT: If 170 damage is too much, the numbers can always be tweaked to something like 100 (+70 Biological)