It wouldn't wreck anything. Tyranids used to have EW in synapse, and when they took it away it made warriors terrible and most games auto-lose when fighting GK. This will give us a fighting chance vs force weapon spam, and make T4 warriors viable again.
I believe they removed EW from Daemons because the entire army gets invuln saves to help them survive things, Tyranids don't have a single invuln anywhere in the codex. Army wide EW will help greatly.