Some requirements:

Better HDRE data JS object

Instead of a strange object with fields like header (??) and _envs (????), what about an object with all the info, descriptive names, etc, like size, num_channels, and skip useless fields like signatura (???).

Data object have to be easy to use to others, not easy to code for you, remember that the file format should never impose an object representation of the data. The data object is the important element, the file format is just a medium.

Also, instead of returning a generic JS object, what about returning a class like HDREImage object? with some methods like toTexture(), flipY() etc.

Remove any flip Y requirement

All cubemaps must be stored in a way that are direct to upload to the GPU without requiring to flipY (as firefox do not supports it and it is very slow to do it manually).

Spherical harmonics

Force that all files must have ALWAYS spherical harmonics, and be sure no HDRE in the database doesnt have them.

Creating HDRE from the library itself

Currently you need to use HDR4EU Studio to create them. But I may have a regular HDR cubemap, or a EXT image, and I want to create my HDRE file from my application (for instance to create reflection probes of realtime rendered scenes).

I need an easy way to call HDRE.createHDRE( texture ) passing the texture and get the HDRETexture object. If it require to include an EXR library it is ok.

Include shader snippets

Add some shader examples in the library to make it easy for people to include, like:

HDRE.shader_read_cubemap = " vec3 readCubemap( samplerCube texture, float roughness ) .... ";