Weather or not Rotorua is most popular and attractive is beside the point. (IMO Southern Lakes District is!).
What matters is the feasbility of rehabilitating the old Rotorua branch or better spending the money helping to build a new route back through to Te Puke...
Tokoroa got a mention as a commuter service potential for the future. This line was once the Taupo Totara Timber Co's private 'light railway' from Putaruru and nearly actually got there (Taupo) at the turn of last century.
The Silver Fern 'Fujiama Twinset' railcars are 38 years old, still going well, a testiment to quality Japanese engineering...BUT...stupidly, the poli's of the time only ordered three. The original suggestion was for ten.
A new type of light bodied DMU that can cover ALL avaliable lines in NZ needs to be investigated. Even now, if they had've survived, the Drewy Twinsets would be 59 years old and even by now most would be scrapped. A Valcan type singular unit with access end doors may be more versitile for 'light' services but a twinset is the best way to go for all.
Indeed the TTT's main line did get to I beleive 15 miles or so from Taupo, but it was a light railway with slow speeds stiff grades and tight curves. Parts of the old alignment were upgraded to become private logging roads serving the Kinleith Mill. I would think that if Tokoroa ever got a passenger rail service then it would be a park and ride off any service to Tauranga or Rotorua. However driving to a park and ride at Cambridge would possibly be the best option.
I do not recall anyone ever suggesting that there should have been 10 Silverfern railcars, I beleive that the dept wanted 5, this would have given 2 in mu each way at hoilday times with 1 spare. But this was witled down to 3.
At about the same time there was a proposal to build 10 single unit railcars for a few of the provincal services that showed the best passenger no.s and 1 of the then withdrawn Standard cars was to be made available to test out the drive train before construction started. I think I have still got the clipping from teh Eveneing post about this. The NZR was at the time disenchanted with the whole consept of under floor engines and articulation thanks to the Drewery cars.
However in reality the buusiness concept of the Drewery Twin sets was almost spot on even today except for the lack of end doors making crewing cost high when running in mu. The truth is that the Standards and the Drewery cars cpould take corners faster than anything else because of teh low center of gravity, this being important on NZ twisted track. Remenber the old jokes about the contractors who built the railways were paid by the curve. Indeed there were offers and proposals to re-engin the drewery cars, but it was NZR and Government policy to withdraw from passenger services except for Auckland Wellington, Chch Invergargill and much reduced subbie services at Auckland and Wellington. In a way tehy were right as to keep long distance passenger services viable a great deal would have been required to realign the tracks and the revenue from passenger services did not make it viable. Now of course much of this work is required to make freight trains competative. If only the NZR had more foresight in this matter.
Indeed my suggestion for any future intercity stock would be single underfloor engined cars with end doors and a driving cab at one end. These would normally operate in pairs back to back or triple sets. Commercialy these would still be marginal and there are few routes where suffecient use would be made to justify the track upgrades to provide competative timings. And that is the killer. If the train is slower than the bus then everybody will take the bus. So the only places you can start looking for suitable routes is where the road journey is very slow. That would be in and out of Auckland and Wellington at peak times, Masterton Wellington at any time and well can't think of anything else.
As for rotes where investment in infrastructure to increase speeds, Auckland and Hamilton is the only one where there could be sufficent demand to amke it worth while at present. However Hamilton Tauranga may become viable once Auckalnd Hamilton has progressed and Hamilton doubles in size. Chch Dunedin may also present an opertunity oif and when the hills north of Dunedin have been tackled for other purposes.