So I understand this is a big ask in part because there really isn’t a standard way to present these chords in roman numeral notation, but semantic slash chords would be super useful to describe things like lament bass and line cliches more accurately in the lead sheet notation part.
For example, consider the sequence Am - Am/G - Am/F - Am/E. In hookpad we cannot enter the third chord as Am/F, we must incorrectly label it Fmaj7. Or take the sequence Am - Bm/A - C/A - D/A which must be entered as Am - Bm/A - Am7 - D/A. In both these examples, the option to use a semantic slash chord would increase clarity significantly. But it might require some nonstandard roman numeral analysis.
In addition, there are slash chords which don’t have true enharmonic equivalents! Consider the “soul dominant” chord ie F/G in the key of C as one of the most common examples. Essentially an inverted F(add9). By entering V11 we get something that presents as F/G in lead sheet notation, but the playback and guide has a B and D in it that we may not want as well. (Really it’s more of an F major over G major polychord here rather than a true slash chord, when played as a full V11, so I would actually argue the current label is actually wrong.)
Even if it had to be done through the “search” feature exclusively, being able to put any arbitrary bass note under any chord without having to work out an enharmonic equivalent that has less semantic meaning would be a very powerful upgrade to hookpad, for both composers and transcribers.