well daura-surwal comes from the times of PN shah and malla kings.It was the warrior costume  in whole himalayan range modified from the rajastani chola.But thenafter it became nepali .the gorkhali fauj wore it  and does still today.So the ones in terai/madhes dont feel any association with it.It has actually nothing to do with [Disallowed String for - castist reference]s except the fact that nowadays most govt officials and politicans wear daura surwal.
Yes this dress was "incouraged" by mahendra but the dress itself predates even the united nepal under the shahs.