Honestly, I think the only modification needed to Surecast is that it should allow a single spell to be casted while in movement. It's not even useful in PvP because you can just line of sight the caster or stun / silence them.

For those saying it just becomes similar to Swiftcast:
1) That's not a bad thing.
2) They are still different. One is still requiring you to complete the full cast time of the action, while the other one is disregarding cast time entirely.

Potential balance solution would be to increase the cast time of the next skill casted. Surecast wears off as soon as a skill is used. (Thus canceling its ability if you want to)