In the savage landscapes of PlayerUnknown's Battlegrounds (PUBG), where survival reigns supreme, the idea of an "Instant Kill" mechanic could shift the entire combat paradigm. Every confrontation, regardless of a player's equipment or strategy, would suddenly hold the potential to be their last.

Imagining "Instant Kill" in PUBG

1. Conceptual Definition: Within the perilous terrains of PUBG, an Instant Kill might manifest as a one-shot, one-kill mechanism, taking down adversaries regardless of their health, armor, or helmet level.
2. Weapons & Gear: Potentially, certain legendary or rare weapons might come imbued with Instant Kill capabilities. Alternatively, specific ammunition or attachments might grant regular firearms this potent trait.

Tactical Evolution on the Battleground

1. Ambush & Evasion Gameplay: The possibility of Instant Kills would further stress the importance of tactics such as ambushing and positioning. Players would need to be even more aware of their surroundings to avoid getting caught off guard.
2. Sniper's Role Amplification: Snipers, already formidable in PUBG, would become forces of nature, capable of deciding the outcome of matches with a single bullet.
3. Loot Priority Shift: The rush to find and secure Instant Kill weapons or gear would likely redefine loot priorities, making certain zones hotspots of early-game action.

Anticipated Player Feedback

1. Mixed Reception: While some might relish the heightened stakes, others could find the mechanic too punishing, especially when losing high-tier gear to a single shot.
2. Tactical Debates: Forums, streams, and chats would burst with discussions about the best strategies to wield or counter Instant Kill potentials.
3. Lore Speculation: Integrating such a powerful feature would prompt players to speculate on its in-game origins, potentially tying it to some arcane lore or an experimental military project.

PUBG Corp's Implementation Considerations

1. Ensuring Fair Play: Introducing a feature with such magnitude would require careful calibration to ensure it doesn't destabilize the game's delicate balance.
2. Limited-Time Modes (LTM): A sensible approach might be to trial the Instant Kill mechanic in LTM, gauging player reactions and gameplay implications before a broader rollout.

Final Thoughts

While PUBG thrives on its gritty realism and tense shootouts, the introduction of an Instant Kill mechanic would push this tension to its zenith. Every decision, movement, and shot would carry unprecedented weight. If ever embraced, this feature would undeniably redefine PUBG's survival ethos.