Would it be too imba if sentry can hallucinate buildings. In pvp would be awesome i think, because atleast jukes would be top notch, but other races … Maybe if you watch the sentry energy or somethings.
This is not balance whine, not some race need buff/nerf, just I think about halluciantion options 
I think this is cool and innovative idea.
Now about the impacts: The best use for it would IMO be denying scouting by showing multiple tech structures. This would work best in mid to high levels of players because low levels don’t scout and the highest levels would most likely be able to call the bluff based on timing,opponent and the like.
Could be also used in other ways like faking bases and stuff.
The biggest downside I think would be the fact that Observers, Overseers and Scans would reveal it as fake.
So overall it could be an interesting gimmick but I’m not sure it would be used very often
So forcefields?..
I think he’s going more along the lines of providing misinformation. Like say the enemy scouts a proxy. Then it turns out to be a hallucination. Then they’re out of position and like “wtf.” I think it’s imbalanced in the case where the opponent is scouting with a unit and sees all 3 tech structures (stargate/twilight council/robotics facility) and then doesn’t know how to react. It’d be dangerous to have early game.
This would just lead to scouting at different times.
Shrooms are probably the best option, head trauma from banging your head into the keyboard (aka zerg “micro”) works too.