It could be any of the engine and/or gearbox mounts allowing movement.
Exactly how much play on your knob are you experiencing? Never thought I'd ask another bloke that question....
The bushes are rubber. They get old, they dry out and they deteriorate. Sometimes they crumbled, sometimes the split completely. Sometimes they just wear and wear and the holes get larger and things get a bit slack.
If the problem is particularly acute I would expect you to be able to jump on and off the accelerator in low gears and for you to be able to hear the engine knock back and forth in it's mounts. You should also feel this movement in drive line shunt as the motion of the engine moves the engine ahead of the drive train. That would give a noticeable yo-yo see-saw like effect to driving that you would feel when you apply or lift off throttle.
Remember, the gear stick is probably all of about 2 inches long below the pivot point. Above the pivot point is probably a good 12-14 inches, so milometers of movement in the engine bay will be accentuated to centimeters of movement in your knob.
I would say that as things get older and elements begin to wear, whilst play is not entirely desirable, the emergence and onset of some movement and is entirely probably and somewhat likely. If it isn't causing gear selection issues or jumping out of gear I would not be inclined to chase the problem particularly. It's simply not worth it.
The particular element you've already replaced, which Fiat call "Rod", I had fail on my Alfa GTA (3.2 liter V6). The design of "Rod" is virtually identical to what you see on your engine. I suspect it failed because the garage did not adequately support the engine when they dropped the sub-frame to replace the ARB, but that's another matter. That let the engine hang forward, stressing the "Rod" bush, tearing it under the weight of the motor. The affects of this failure were immediately obvious, i could feel the engine rocking on throttle with a noticeable clunk at it reached the extremes of it's travel. I don't recall any movement in my knob so much as I did the movement in the motor though.