• The first problem is that when first taken in hand, one can't tell what ritual was selected, and selecting a ritual requires clicking through potentially the entire list. The ideal would be a GUI, but if this is not reasonable, it would be nice for the diviner to "flash" (HUD text) what ritual it's currently set to when it is selected as tool-in-hand.
• The second problem is that the diviner's ghost blocks vanish the moment you look away from the MRS, which for large rituals makes it very difficult to see what blocks are occluded. Perhaps they could persist for a given length of time (15 seconds?). Better yet: Let them persist until (1) the diviner is no longer the tool-in-hand (the player would need to look at the MRS again after re-wielding it), (2) a different ritual is selected, or (3) the player moves a sufficient distance away (16 blocks?)
• And for the Tweaker: When using the Ritual Tweaker to set areas, it would be very helpful for it to show lines, or at least corners for what the current area is. As with the diviner, flashing a tip on wielding for its current mode would also be nice, as would a message giving the restrictions for the area to be set (e.g., "The area must be entirely within 15 blocks of the MRS").

The ideal would be a GUI

Ehhh... No...

The second problem is that the diviner's ghost blocks vanish the moment you look away from the MRS, which for large rituals makes it very difficult to see what blocks are occluded. Perhaps they could persist for a given length of time (15 seconds?), or until the diviner is no longer the tool-in-hand.

Shift right click on the MRS to bind the ghost blocks to it.

OK, that beats my complex persistence ideas.