I like this theory a lot. I was thinking along similar lines about the use of color, how easily forgettable and seemingly peripheral to the magic it is, yet it would be unlike Brandon to include something that wasn't absolutely necessary and there for good reason! I hadn't put together that each magic system could have three parts, but this feels right to me and matches what we know about the three realms.
I do not agree about touching being the physical component on Roshar, though. Prior to reading this thread, I was thinking about the similarities between metal, color, and Stormlight:
- All commonly exist in the world, but are inert until activated by a magic user.
- All are consumed when magic is performed.
- Magic cannot be done without them. Vin with no metal, Vasher with no color, or Szeth with no Stormlight, are all equally helpless.
- All can be stored in some way, and are frequently carried around by magic users. Metal in vials or inside the body, Awakeners wearing colorful scarves, Stormlight captured in gemstones or (rarely and imperfectly) inside the body.
I'm less clear on this, but I also see parallels between Breath and spren. Intangible things, somehow important in activating magic, not themselves sentient but somehow linked to sentience or enhance it in some way. The way all spren are identical and have no memories, but then Syl develops a unique personality after becoming attached to Kaladin, reminds me of how Breath can be transferred between people, but it does not transfer specific memories or abilities while doing so (all Breaths are fundamentally alike, in the same way as all spren?) I don't feel like we understand enough about spren to judge if this is a true similarity, but will be interested to keep it in mind as we learn more.