I would want to be able to choose what pressure is affecting (size, opacity, or both or NONE - none being very important especially since Tagtool is designed to effect these things with our offhand). Overall, since the left hand does the heavy lifting of changing settings, I think that being able to reduce the load of our offhand by choosing what the pressure affects is really important as is just removing the pressure sensitivity altogether and using the pencil for better drawing accuracy. Here's a video of options provided in procreate (most widely used iPad Pro drawing program which is why I reference it):
Also slightly off topic but worth mentioning in the same thread: I've always found the look of the Tagtool brush a bit biased towards a "cartoony" feel. Has there ever been consideration to adding a few brush types (like you find in drawing programs like procreate) to the program? Even just a very classic photoshop style pencil or a rounded brush (with none of the circular marks indicating rotation that the Tagtool brush creates) would be nice.