I should say that importing large tilesets into world partition directly isn’t impossible, but it seems limited by resources. With an Epyc CPU, loads of RAM, and a Radeon Pro SSG (the GPU with an NVMe drive expanding the VRAM), I expect you could import a very large tileset.
With the recent release of DirectStorage, it might be possible to expand VRAM to the point you could import the whole tileset. Once it’s in and you’ve set up streaming in editor, theoretically you shouldn’t need the whole thing loaded? World partition doesn’t load the entire terrain at once afaik. I’ll explore this solution soon.