I have OH1.8.3 runningy satisfyingly. Now I’m on the migration, incl. migration to a new machine.
In order to keep my OH1.x version stable/untouched I was thinking of buying a 2nd zwave Aeon Stick and connect it with the new machine.
Is it possible that all my zwave devices can report to 2 controllers?
As is often the case, the answer isn’t a simple yes or now - so let’s say, sometimes 
It will depend on the device - in general, the answer is that you will be able to make some things work, but others won’t. For example, you can only set one wakeup controller - so one system won’t work well with battery devices. Lifeline association groups used for reporting state changes to the controller tend to only allow one controller to be configured (although some devices do allow more nodes), but you might be able to offset this, at least in part, by using different association groups.
You’ll almost certainly be able to control most devices from both systems, but it’s almost just as certain that you won’t be able to get everything working 100% from both.