Victini does produce infinite energy, but it's also said to bring victory to anyone that owns it so I doubt the idea of using it as a power source would be a primary reason for Team Plasma to seek it out in a remake, especially since their goals are to disarm every Trainer in Unova and then rule over it with the aid of a legendary Pokemon. They never were after infinite energy to start with.
The idea that they never run out of power because they're infused with IE opens up some holes though. For Mega Stones to constantly be full of energy they would have to be ridiculously unstable, therefore making their use very dangerous, and it brings up the question of why they themselves were never researched as a power source. It also doesn't make much sense if you think about it, because they're not just simply radioactive rocks. Evolution stones do emit radiation that causes certain Pokemon to evolve if put in direct exposure to them, but it only has enough power for a single evolution; after that it runs out, which is likely why it vanishes when used. Mega Stones were made from being infused from purest lifeforce essentially, but should logically operate in a similar way, as they shouldn't just be able to put out an infinite, constant stream of lifeforce energy unless they were living things themselves. It's like finding a fuel source that is never used up no matter what. Even nuclear rods used in fission eventually burn out, and since very few if any Pokemon produce infinite amounts of IE, Mega Stones should eventually lose their evolution-inducing properties unless they were being refilled with each use.
But then again Mega Stones are incredibly odd to say the least. Mewtwo was a recently created Pokemon, and yet there exists not one but two Mega Stones for it, both which were presumably created a very long time ago. And technically there shouldn't need to be any Trainer interaction at all, since if they're constantly emitting energy just holding the stone should be enough for a successful Mega Evolution attempt. How does the Key Stone work? Is the Trainer's own life energy activating the Mega Stone, being amplified through the Key Stone?
