Shipping textures as PNGs is suboptimal

Any modern engine does this automatically on PNG import, or as part of material/shader setup. You want different formats for different things, e.g AO, normals, bcs different formats have different compression artifacts.

How much extra time does it add for startup? For a single texture it’s probably negotiable but for a modern game, we’re talking about thousands of textures, so maybe it adds up?

If you’re compressing at load-time it can be a lot. You can do a quick and dirty compress to BC1-3 (assuming you are on PC) in a few tens of milliseconds but quality will be suboptimal, higher quality will likely take a few seconds per texture and going to BC6 takes even longer but will look much better.

> higher quality will likely take a few seconds per texture

It takes that long to do a good compression on the format that interpolates 2 colors for each 4x4 block? Huh.