Thanks for the info. For me personally (maybe others agree...) the space bar is the best option as auto replace trigger to preserve coding flow. This preference is the reason, why I was asking.
But I checked some other single keys (without Ctrl or Alt) even with Shift as keyboard shortcut, but all of them also trigger the respective key action in addition to the auto replacement.
As you said, it is also possible with key + Ctrl/Alt, but I think this distinctly interferes with the typing flow at that point. Partly a question of taste of course, but maybe this could be worth another improvement...