Is there any good way to produce a time signature in text? Like, imagine a tempo marking of “Gradually faster until start of 3/8” or something
In a tempo entered via the popover, no. The popover only accepts plain text and there are no formatting options available.
You can enter the “tempo” as System Text and use glyphs (under the ligature section I believe) from the following page (which you can simply copy and paste) to make the time signature. You would need to set the glyphs using the Music Text Character Style, which is the top-left of the text editor.
The lack of formatting in tempo (and other text) is a real bummer. I often see scores with for instance, and original tempo marking in the original text, and then a translated marking, in either english or italian, beneath in italics.
This is true. Using system text is more-or-less fine except that, not being a true tempo, it doesn’t automatically align with time signatures. But some discontent with tempo inflexibility has been noted before.