Love a Renarin heavy ep! I have to agree with @FeatherWriter on illumination. I think he is has progression, illumination and the void surge. Mainly because the light he makes when battling the Thundercaste sounds like what Ym's non-corrupted Truthwatcher spren wanted him to make. But I also think that it sets up something really facinating if he does because if illumination is of honour (I am not sure) then Renarin could have surges for all the Rosharian shards. Which would have to be significant.
I do suspect that the fused recognised Renarin as a fellow void-binder. The how is the interesting question.