I kept running into the same problem. I had a flat SVG and wanted to see it rotated in isometric space. Every time I ended up faking it in Figma or eyeballing it by hand.
So I decided to build a tool that can take any SVG, freely rotate it in isometric/orthographic space, and keep everything as clean vectors.
...and got a bit carried away.
Still a work in progress. Access is limited while I build things out. Drop your email and I'll send a code when there's a spot. Follow @brdrck for updates.