In principle, I think the GK / TI countdown has the potential to be just as effective as the GK 8 second one. However, as with that change, the devil will be in the detail as we aim for consistency regarding if / when to start the count. I really hope that this detail is spelled out for clubs and referees alike.
If it was down to me, then I'd set the expectation as 1) if a nearby player is jogging to get the ball and get to the point of the restart, all good. If not, start the count. 2) assuming count has not already started, once the player is in position, ready to restart, start an 8 second count in your head and start a visual count at 5 if required. Overall, this would keep things relatively consistent with the current 8 second count and take into account that the time to retrieve the ball and get to the point of restart will inevitably vary from situation to situation.