Definitely think heavy rail is the way to go on the NWTC. The ultimate idea for me would be a branch off CRR at Roma St and a tunnel out to Everton Park with stations at Kelvin Grove, Newmarket Shops and Alderley. It would use the corridor and eventually join the existing Caboolture line again. I’m not 100% sure what the best option would be. One would be to have it join at a new Fitzgibbon station located around Linkfield Road. The downside to this would be that it would take slots from the CRR core heading north. These would ultimately have to be replaced by services through the existing core.
I think you could also include options like 4 tracks in some sections north of Everton Park to allow express services for further north. Alternatively, you could just have the line terminate at Roma St on a pair of new platform. I think the buses could do so much more with a train line to feed into. A train from Roma St to Everton Park could do the journey in around 10 mins or so. This is far quicker than what any bus could achieve. I’m a firm believer that generally speaking, buses should feed into or connect with trains in the further out suburbs (old zone 4 and 5 - outer current zone 2).