Train falls under KR. KR is not an official zone of IR, hence it has to take coaches from other zones for maintaining its rolling stock. Hence, these coaches won't be replaced unless and until 25 years I guess except for POH and IOH. Still the interiors are quite good compared to many other trains of IR. Though I agree exteriors are not upto the mark.
And regarding the RSA concept, it was introduced as there is shortage of coaches and still it's a good method to cut on costs and use d resources to optimum.