I wanted to suggest some features related to usability/exporting. I did scan through the roadmap and didn't see these, so hopefully I'm not repeating anything that's been said before.
When you have a slice that's created from a layer, perhaps it should output the layer even if the layer has visibility turned off (otherwise the created file is just blank). It would be useful to be able to create a slice that includes multiple layers within it. (Sort-of related) The ability to toggle visibility on more than one layer at a time.
These are things I've been finding when building files with embedded text that has to be in foreign languages. I make a layer group for each language, and create slices based off of those, but I need to duplicate the graphic elements in the layer groups. For example:
Layer groupLogo
Translated text
Layer groupLogo
Translated text
This is fine for now, but if I need to change the logo, I'll need to do it one time for each language...not good. So similar to the way you can create a slice from a layer, and it disregards all but that layer, it would be great to be able to create a slice from multiple layers, and it disregards all but those layers. Then I can just have a "graphics" layer, and then a text layer for each language, and slice them accordingly.
Also, when I'm working in the document, I tend to want to make all of the language-layers invisible except the one I'm working with. But when I go to export, I have to remember to turn them all back on so that the slices aren't outputting empty PNG files. Whoops! So I figure, if i have a slice based on a single layer, and that layer's invisible--it should either warn me when I go to export, or just treat the layer as visible for the purpose of exporting. Make sense?
Finally, I also find myself wanting to select several layers and then toggle the visibility on them. On a Mac, I believe the ALT key is used to select/deselect many checkboxes at once, and to open/close many folders at once. Maybe holding ALT while toggling visibility makes it affect all selected layers?
Anyway, I know that the Serif team is hard at work adding more stuff, and I really appreciate it. I've never been able to break into Photoshop or Illustrator, but Affinity had me from hello.