Thanks, Ben!

I'm using Ext3 still.

Like I said, I ended up per Matt's suggestion decoding data on load, like you suggested in 1) (not sure why I would care if there is a guarantee my listener will be called before other load listeners...)

I did try fiddling with it like you mentioned in 2), but to no success: there is indeed 'metachange' even being fired by the store, but AFTER all reconfiguration already took place:

            if(this.reader.onMetaChange){
                this.reader.onMetaChange = this.reader.onMetaChange.createSequence(this.onMetaChange, this);
            }

where DataReader's this.reader.onMetaChange deletes the configuration from the passed in configs and reconfigures it based on the received metadata, then Store's this.onMetaChange fires the 'metachange' event. So I'm not sure what the proper approach here should be...