Happy to see this topic, as this list is something I've been trying to figure out for awhile now. I think we've been given hints from the very beginning by the list of ten essences that exist in the Ars Arcanum of the books (or here: https://coppermind.net/wiki/Ten_Essences). Pay particular attention to the "Essence" or "Soulcasting Properties" or "Divine Attributes" columns. For example, 'zephyr' is defined as a light wind, and 'transparent gas/air', which both fit in with windspren for Windrunners.
Some of these are not obvious. For example - Elsecallers essence is 'Tallow' - what does that have to do with inkspren? Well, tallow, wax, soap, and similar substances were often ingredients in the making of ink. For the divine attributes, 'wise' and 'careful' thought could be defined as logic, so 'logicspren' would fit well.
Releasers have a 'listed Body focus' of 'the soul' so maybe the name 'Releasers' has something to do with releasing the soul of things? It seems likely that their mascot is flamespren.
Willshapers have essence/properties of foil/metal, and I'm not sure where to go with that. Mirrorspren? Doesn't seem likely. Maybe something to do with forging or smithing? One of their attributes is building. Kelek, the representative Herald of the order, is mentioned as teaching how to cast bronze at the beginning of desolations.
And so on. Lots of information to play with.
