The icon files themselves are there, they're called "actualiconname.b4bfb144.png". I don't know if that is wanted or not, but they definitely are not used. Changing the resource strings in SteamVR/drivers/indexhmd/resources/driver.vrresources to have that additional ".b4bfb144" makes the new icons appear as expected.

A very minor bug but also easily fixable in a minute.