Slide notes are really nice feature, but they make the note data look a bit messy when you have a lot of them. Another downside they have it that they slide the pitch/volume linearly, while sometimes you might want to make different shapes. For that reason I think that replacing slide notes (or adding alongside) with lines that represent the pitch motion. Fundamentally they would work the same way automation clips/line editors would. You could add points, delete them, change line type and so on. Editing these lines would be a tool of it's own. When in use you can't interact with the notes themselves. The lines would be tied to the notes so if you move the note, the lines move with it. Additionally, the could snap to the grid to keep the notes in tune/time more easily and could be temporarily disabled by holding Alt similar to how you do in line editors.
Very simple representation of slide notes vs. pitch lines and how they look
[Piano Roll] Pitch lines/curves
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[Piano Roll] Pitch lines/curves
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