In Cubase Pro there is a feature to record tempo changes (Ops Manual pg. 928) which sounds enticing but in its current implementation is nearly useless. Basically it is a slider that you can drag back & forth to write Tempo Track data during playback. According to the manual,
This is useful if you want to create natural sounding ritardandos, for example.
But the problem is you don’t hear the tempo changes until you stop/restart playback. Without audio feedback when using the slider, you are unlikely to create a “natural sounding” anything.
Two changes would convert this feature from an interesting concept into a useful tool.
Adjust the playback tempo in real time when using the slider so you can hear the actual changes while you’re making them. This is really crucial to making this feature useful.
Let the slider be assigned to a Quick Control. This would let you subtly adjust the tempo throughout a piece by turning a knob - almost like conducting.