You are right about 3D printing fundamentally changing our hobby. With wheels the trick will be marrying the tyre to the centre. Unless somewhere out there is a metallic resin or filament to print the whole wheel.
I remember a couple of years back reading on a forum about someone who was trying to print their own track – including the rails!
You raise a couple of different, but related points. Both of them have been discussed recently on the Scalefour Society Forum.
In relation to 3D printing of wheel centres in a metallic compound, then this is the way that 2mm Finescale modelling is developing (I’m a member of that society as well, because it is where a lot of cutting edge technology and techniques can be found). The latest wheelsets are 3D printed in metal, which is perfect for the 2FS approach of split axle chassis. https://www.scalefour.org/forum/viewtopic.php?f=40&t=5859&p=99414#p99414
The only downside is the cost: for 2mm driving wheels you are looking at something like £12-15 an axle, from memory. When the topic came up for them as a P4 route, it was pointed out that you would be scaling up all dimensions and using eight times the material. A cost of around £100 an axle anyone?
Now like any emerging technology, the cost per unit will come down, but for the moment it would be beyond the reasonableness of 4mm modellers.
For 3D printing of track, this is absolutely now a thing. The current version of Templot will allow the export of a 3D printing file that can be used to produce sleepers, chairs, and even individual keys to suit. This gives all the design flexibility of Templot with a very practical, accurate and timesaving result.
Have a read of https://www.scalefour.org/forum/viewtopic.php?f=5&t=7597