Actually, no problems. The issue was caused by copy/pasting the images in. The user was expecting the pasted image to keep the original file format, but the pasting process converts to TIFF.
However, it would be a nice-to-have if there was some control over the output image format as then users who put in TIFFs could still get web-viewable SVGs if the images were transformed to PNGs.
Also, while I’m thinking of SVGs, having images encoded as data URIs in SVG export would also be a very handy option. This would mean the SVG would be a single file containing all the linked images - no need to save a folder full of files.