Essentially, Simon becomes not just Ion, but every Spectrum Entity/Deity and serves as an INFINITE BATTERY and SUPERCHARGER for their powers, alongside granting each access to his now Source-Spiral Energy, or granting them all the mathematical truth of Life is worth living.
Which is incredibly ironic. The Spiral Nemesis was about how an overabundance and use of Spiral Power would end the Cosmos, and Simon--Through Kyle--Is granted the perfect means to prove the Anti-Spirals wrong and lead the world into ULTIMATE paradise, as he said he would when the Cosmos was entrusted to him. It fulfills the prophecy and breaks past it, which is exactly what Simon (and Kyle) are as characters.