I for one will most likely be getting one if and when funds allow, as something planning to build an LNER themed layout (albeit somewhat removed from recorded history, but that's already been touched on in another thread) it'll be an invaluable addition for replicating the all important heritage railtours similar to the ones ran in the 30s. Now to find some 6 wheel coaching stock...
I could even justify having a larger tender compared to the sturrock tender it's had for a good proportion of its life by the fact that as the atlantics were withdrawn in the 50s it would have most likely been handed down a larger tender similar to the one it would have originally used.
On the subject of a drive train. if I could put my two cents on the matter using two existing RTR Stirling singles in different scales as an example.
When Bachmann in the States produced a model of the character called "Emily" from the show about a certain blue tank engine, said character being clearly based on the Stirling single, they incorporated two different drive systems for OO/HO and G gauge., both of which are rather novel solutions
for OO/HO (the version which I have owned). the front bogie in essence does not exist, the front most leading wheel and the trailing wheel is unpowered and are both free to move about. but the carrying wheel just in front of the drive wheel is powered off of the main drive wheel using a series of idler gears proportioned to make it spin at the correct rate meaning from a technical standpoint it runs as a 2-2-2-2. this has also allowed Bachman to incorporate the skirt below the cylinder without risk of the front bogie clipping it because there is no bogie. a video of it running on a rolling road can be found here:
https://www.youtube.com/watch?v=ZrXH1xWplSo
for the G gauge model. from what I understand. the main drive wheel and the trailing wheel are geared together in a similar manner to the HO model. meaning it operates as a 4-2-2-0 with the tractive equivalent of a 4-4-0.
personally I think that the HO drivetrain would have been the best version to replicate as it would allow for the distinctive skirt and under regular running you can't tell that there's no front bogie because the skirting conceals it anyway