Write support is no problem, I will add this.

From reading the spec in the link you provided I think the implementation in general is OK.

Everything apart WAVE_FORMAT_PCM should have an extension size cbSize, that's right. But only WAVE_FORMAT_EXTENSIBLE sets cbSize=22.
So for read access it is not mandatory to check the value when WAVE_FORMAT_IEEE_FLOAT, but for writing files I would set this to zero.

There are several other wave formats which also use float data, but most important is WAVE_FORMAT_IEEE_FLOAT, and that can be suppoted quite easily without many changes.