I'm torn. On the one hand, it's hard to deny that politically, this tunnel would be very easy to get across the line, and it probably would, at least in the short-to-medium term, alleviate some of the awful traffic along Gympie Rd from Aspley to Lutwyche.
On the other hand, all the money that would be spent on this would be far more effective if it were spent creating a better local transit route. They say:
We are also focusing our efforts on improving public and active transport, including the Northern Transitway
But the Northern Transitway is only buses, and will only operate in peak hours anyway, once you get to Kedron where the existing tunnels end. Imagine if, instead, this money were spent on a light rail system. It could operate with much higher capacity than the buses ever could, and its long-run operation costs would be lower too.