Excellent suggestion, Ragnarok. I completely agree.
You are correct that any spell can be upcasted, even if doesn't benefit from using a higher spell slot. See an explanation, for example,
here (especially the comment about Warlocks).
This logic can also apply when a player clicks on a particular spell slot. If they are out of Level 2 slots and are looking for a cheapest way to cast Misty Step, for example, the
II on the icon will clearly show that they can't do it with SS1, so no point even going there (I'm talking about a post-release situation, of course). This should save them some effort and time.
Yeah, looks like it is viable as a universal approach, regardless of the filters.
P.S. One little correction, however. In your last picture, the Misty Step icon that comes from an item has no numeral on it at all. This might create some confusion for newcomers, because they might think it's somehow castable as a cantrip. As I suggested in your other topic on a similar subject, this icon should instead be placed on a different band within the same hotbar. And once it's there, sure, it can retain its proper numeral (just to designate the spell's relative power, if anything). Same, of course, should apply to scrolls.
