Bad news. Getting crashes with 64x64 tiles involving creature graphics. I don't know exactly what triggers it, but switching body, hair, wearables, wieldables, and saddles back to 32x32 fixes it.
Excluding UI and world map, it looks like everything else can mostly be upscaled fine, except for a display issue when clicking on items like rocks and figurines:
More details about world map and UI issues:
- higher-resolution world map tiles (the ones before embark) work but they are still displayed at their original size, so not much advantage unless it gets displayed differently on a 4K or HiDPI display. Mountain and forest tiles have display issues at different resolutions, though, so they need to stay 32x32
- portraits shouldn't be resized unless you are also resizing the BASIC_FONT at the same percentage as them, or else they won't look right (see imgur link at bottom for demonstration).
User Interface upscaling:
- UI - even though the size of the UI is linked with the size of the BASIC_FONT, even if you use the default BASIC_FONT, you can still get benefit from a higher-resolution UI if you use the upscale interface feature in the video settings.
- Don't change announcement alert size (they will overlap each other if you increase the size)
- Don't change moon weather size (won't scale the same as the rest of the UI)
- (not an exhaustive list of UI issues. needs more research.)
Portrait testing gallery:
https://imgur.com/a/iIyPVbE