Things I'd expect a soulmind's essentia-imbued mindblade to do:
  • Bypass DR as a lawful or chaotic weapon, according to wielder's alignment
  • deal bonus damage vs. foes of opposite alignment (like an axiomatic or anarchic weapon)
  • look cooler

5 bonus essentia from knife to the soul might be a bit much. That's more than a 50% bonus over your unbuffed essential capacity at 13th level. Also, you need to specify the duration of the temporary essentia.