Prototype: Omnistone should "unlock" at levels 9 and 18, permanently granting you a keystone to use
Title. In addition to the constantly rerolling keystone, you should be granted an additional keystone for permanent use at those levels. The way that this keystone is awarded should be determined semi-randomly, weighing in how effectively you used each keystone.
For example, if every time you got arcane comet you managed to land 100% of your comets, it should be weighted higher than the conqueror you never managed to fully stack before it wore off.
This would make the rune go from troll tier to a legitimate mid and late game power spike, having effectively 2 to 3 keystones to use at a time.
The obvious trade off would be the early game power of having a consistent keystone to use.