he's been easy to manipulate in the last few decades is, of itself, odd... but does not take away from the growing unpredictability as the timeline grows
That opens the possibility as to whether Veidt would have thought of manipulating Jon in other, more subtle ways, thinking of him as a more direct tool...
And you realize that his apparent immortality alone makes him unpredictable. His other powers compound that. That.
I think understand what you're saying. While Jon is not necessarily an immediate threat, he sees him as a threat to the long term viability of his vision. Ironically, he's made no visible contingency for succession.
A crystaline time structure... a tachyon interference of unknown time/space determination... and a continuance of a crystaline time structure.
That's certainly Jon's view of time, prior to sharing the removal of his intrinsic field with a certain reegineered Rex Felis
. Yet one of Moore's themes being who makes the world
coupled with I leave it entirely in your hands
seems to indicate that only the past can be set in (crystalline) stone.
Perhaps the crystalline (ie immutable) view of past/present/future as seen by Jon was a function of his lack of exercise of will. When you make no decisions, you have actually decided to go with the flow, and will go wherever the current takes you.
Remember that on Mars, Jon thought the cloudy future was perhaps due to nuclear explosions. When in New York, he opines that the Tachyons are causing his perceptions to be muddy. What if he's wrong about that, too? What if his inability to see the future is because the crystal has not yet formed, but is only potentially still molecules waiting to be interlaced?