I teach coding to designers and we use a lot of SVG files for obvious reasons.
Repl is an almost perfect env for that.
It'd be perfect if we'd have the possibility to check/edit the SVG code, otherwise we have to use an additional text editor, which doesn't make sense.
A year late... but my students have the same issue. An easy work-around for them is to create a .txt file in repl instead of an .svg file. Edit the file as if it was an SVG. Then, change the file extension to *.svg so that it can be properly loaded and recognized as SVG within HTML / SVG / CSS.