Long time followers may remember my project to build a 15xx tank loco. This is as far as I got but this may hopefully change as Warren shepherd who does a kit in 7mm scale is considering a 4mm scale version. http://www.warrenshephard.com/gwr.htm
He needs at least 24 firm sales to make it viable and expressions of interest are being collected on the GWR modellers Facebook group https://www.facebook.com/groups/921387308231483/?ref=share