Going by WTM, currently the most profitable Neoscrypt coin is 15% more profitable than ETH only mining on a weekly average basis. Once you factor in dual mining and the increased difficulty that will come shortly from Vega's, that will certainly make it less profitable, at least for RX 580's.

http://whattomine.com/coins?utf8=%E2%9C%93&adapt_q_280x=0&adapt_q_380=0&adapt_q_fury=0&adapt_q_470=0&adapt_q_480=0&adapt_q_570=0&adapt_q_580=0&adapt_q_vega56=0&adapt_q_vega64=0&adapt_q_750Ti=0&adapt_q_1050Ti=0&adapt_q_10606=0&adapt_q_1070=0&adapt_q_1070Ti=0&adapt_q_1080=0&adapt_q_1080Ti=0ð=true&factor%5Beth_hr%5D=29.0&factor%5Beth_p%5D=150.0&factor%5Bgro_hr%5D=0.0&factor%5Bgro_p%5D=0.0&factor%5Bx11g_hr%5D=0.0&factor%5Bx11g_p%5D=0.0&cn=true&factor%5Bcn_hr%5D=740.0&factor%5Bcn_p%5D=100.0&eq=true&factor%5Beq_hr%5D=318.0&factor%5Beq_p%5D=130.0&factor%5Blrev2_hr%5D=0.0&factor%5Blrev2_p%5D=0.0&ns=true&factor%5Bns_hr%5D=1000.0&factor%5Bns_p%5D=150.0&factor%5Blbry_hr%5D=0.0&factor%5Blbry_p%5D=0.0&factor%5Bbk2b_hr%5D=0.0&factor%5Bbk2b_p%5D=0.0&factor%5Bbk14_hr%5D=0.0&factor%5Bbk14_p%5D=0.0&factor%5Bpas_hr%5D=0.0&factor%5Bpas_p%5D=0.0&factor%5Bskh_hr%5D=0.0&factor%5Bskh_p%5D=0.0&factor%5Bn5_hr%5D=57.0&factor%5Bn5_p%5D=345.0&factor%5Bl2z_hr%5D=420.0&factor%5Bl2z_p%5D=300.0&factor%5Bcost%5D=0.12&sort=Profit&volume=0&revenue=current&factor%5Bexchanges%5D%5B%5D=&factor%5Bexchanges%5D%5B%5D=bittrex&factor%5Bexchanges%5D%5B%5D=cryptopia&factor%5Bexchanges%5D%5B%5D=poloniex&dataset=&commit=Calculate