I looked over Wowhead and Icy-Veins, downloaded some Weakauras and did some optimization on test dummies. The macro has the option to be especially lazy by focusing the tank in dungeons and this simply puts DPS on his/her target.
Update 1/17/21
Now that I have my Shadow Priest up to ilvl 200, I’ve messed around a bit with my talents and these macros and updated them to produce more DPS. Here are the updated versions:
Single-target
d0ZYcaWsvL6TOW2qjxw0mbOdRYSPupgPBsb)Ik(Mqf3Ja2PQSxLDJQ9d1PH0FvvPFt04KkdfqgmIHluoifY0OshtkhNGAHQQYsvvvlgLA5cEOQkEQKLrvRtOQMie1uPKjRQOPt6IaPRQQGNrrxxiBuOkBLGSzGQTtHYhvvYxfQ0NbIHjvnsvf6CqKrduEoOtsGMfG6Ae68a4UOOBdHxtHQxBw71wvF0iK)Te89fGG(Rbq))N98ZAL1zNCfUQ59MnFBLrrkyYWkdzGU6RcuHYaevY3ZZYTTYWXJoBb5AgmwYvujF)TYWrdsHYaevYHZAV2S2RTYHEqfMchLCAIjysiHPkavIG9PycM01JKFp)kh6bvmX0u0LvC2ZCLd9GkMWGlPGDCEAJYbHjMy66AAUN7kh6bvmHbvIG9PmXKMOVJ1EIRCOhuHPWrjNMycdUKc2X5PnkheMysiHPkavIG9PycMi2jcmMi2jcmMi2jcmMy6IuZDfGszmarrGQRAR(ob4)0opyoR9ARCOhuXegujc2NYete7yTNFLd9GkM49DEw9tx9DcaqHecN1ETvoheIcvmbCjncUNFLd9GkMWaCzar87zIjEtplK62ZCLd9Gkmfok50etWKqctva9cGKkMGjMUi1Cbgt4r22txvAglErCQIk5RakGkdOkaRakKgoAqoR9ARCOhuXegCjfSJZtBuoimzqLiyFktmP13ZQF6kGKq1WrdYznD60viNGFr26ETvaEq9dX(808Zv(EFRV179ExrV7kHUa6X2oHZA6Qkwsfe598IDRIBEg3OOWbN10vGYbxgO5pseXo9yJAJQaS)MoDd
Multi-target
d0d0caWsa0BHQ2gQ4YIMji5WQmBs1Jr5MOs)IkUnOCEG0ovL9kTBc7hXPHYFbi)MKHrKHcedgPHluoiQQMMQ6yk5Cavleq1sbKwmOA5cEiG4PkwgvToHknruftLOMma10PCrsrxfq5zuPRlKnskLTIQYMbrBNuQ(iaywGWNbkphYifQY4uQgni1RfQ4KOk9vaORPuUhPK7cvooPW3eQQ7QY9T6mXJFEaexGbLmVaIRMafi95RCh5tpfgQZY7Dx(vh(JmOvHoCZaRdamAYxgqykrFEo)vhUNi605vyzq7PWWuIc8oAkGufyjquWID2bhthZaTaVdpjKxKU13QduhYawmaFwc4oEj)sAj59()M)3HVlGDW1tuLR1zILmE5Pp)2EhamV4WFu4qvUwhUhlO4ldimLav5(wvUVvhh2HmuQrukyjHsOHeLMwmfm4NrOe6Ue4((8DCyhYiux3TpN43NBhh2HmcfVqXG(eIuhtagoc19)DD773XHDiJqXZuWGFgocDT53503whh2HmuQrukyjHIxOyqFcrQJjadhHgsuAAXuWGFgHsO)DP)gee6Fx6VbbH(3L(BqqOUFWx)oqPuXGcdgM1z1bGjOan1ZdLvUVvhh2Hmcfptbd(z4i0TDo9574WoKrOE)UNJuToambfKqIqvUVvhNdHWqgHcPIfH6Z3XHDiJqXdPkalUs4iuVRNd47952XHDidLAeLcwsOeAirPPLDbWsJqju3p4RpeeQisxVwhquiJ7XcQkxRdiHK7XcQk33QJd7qgHIxOyqFcrQJjadhEMcg8ZWrOljjos16mwgtBrcMHPeDajGPcygO1QvRwl
Old versions from Nov 2020 for posterity:
Single-target
dWdgdaWseO3QQ8AcQzsbomWSjYJH6Muu)IO(MkvDoLu7uf7vA3OSFq3Jc5Vii)gvNwvgQsyWqgovXbrqnok1Xi0bhthZaTaVdpjKxKU13QduhYawmaFwc4oEj)sAj59()M)3HVlGDW1tuLR1zILmE5Pp)2EhamV4WFu4qvUwhUhlO4ldimLav5(wvUVvhh2HmuQrukyjHsOHeLMwmfm4NrOe6Ue4((8DCyhYiux3TpN43NBhh2HmcfVqXG(eIuhtagoc19)DD773XHDiJqXZuWGFgocDT53503whh2HmuQrukyjHIxOyqFcrQJjadhHgsuAAXuWGFgHsO)DP)gee6Fx6VbbH(3L(BqqOUFWx)oqPuXGcdgM1z1bGjOan1ZdLvUVvhh2Hmcfptbd(z4i0TDo9574WoKrOE)UNJuToambfKqIqvUVvhNdHWqgHcPIfH6Z3XHDiJqXdPkalUs4iuVRNd47952XHDidLAeLcwsOeAirPPLDbWsJqju3p4RpeeQisxVwhquiJ7XcQkxRdiHK7XcQk33QJd7qgHIxOyqFcrQJjadhEMcg8ZWrOljjos16mwgtBrcMHPeDajGPcygO1QvRwlXPiwOs0sjiwSsz5I6HuqpvyzuzDQuPjsHAQuYLvmDsxerAykjptKUUkzJQuXwPiTzvkBNQu(icywiIpJO8DQs1iPk5UQQgnIQPrGtIq2Ms11eX5rOwjbPNJ0TPQUI1QhXgHxe2ycfeDiGbKsiZKked7XvRgEnsEKEmHB0WcinmL2q05sfDInmdWzUPtM(4mAT6rSw9i2qgdOkDm5Ay4bIGO8qh1im3FdOqeezVATRhxdzmGQq0hM7Vb0FiY5SD7R6jTHmgqviknnrW(99iOHmgqvi6JXXKdySr6Xi7hIsfiinTNKgYyavHOpm3FdO)qKyIZEVN9gYyavHOpghtoGXgPhJS)pm3FdO)q0cU3Nmere72f9Xz9CFdzmGQ0XKRHHhi6JXXKdySr6Xi7hIYdDuJWC)nGcrquIDcjquIDcjquIDcjquQG1Ic6XUHmgqvi6dZ93a6pe5wV7wz3Wao3Jbp)N2OXcovndWzETQ2WqU)gq7YgeCiwiJ0aOtT6rSHmgqvi6dZ93a6peLyV3JRHmgqviY5SD7RQ2GGdXlYdLwREeBidO0hvHOBC8fThxdzmGQq03nE2)UR(HixQBFTDpPnKXaQshtUggEGiikp0rnsbzYgfIGOubRffqceXUKKQ2i0XZDUyy9XznwKF88tjUHv(XeEuXUSXI8ygGZ8AvTHv(XeEuxxwTAdceKA6KPpoRh3UBVHza7ciretNS3gM(4SUSbHVuY55gMNmUHxJKNgqH2W45g4ss7rSHPG8dSjn0AvTr4zWezCpUe7gKYUXZ4XqUVhGc2EspL4USA1wa
Multi-target
d0thdaWseK3QQSnLYHbMjPspgQztuVwj4MKWViPVHaUhjQDQk7vA3OSFqNwL(lQu(nHXrLgQsYGHmCQOdIaDzfhdvDovKfQKAPiOwSkSCHEivONkAzu16uczIKkMkPmme10PCrQGRQIsptqxxPAJQOYwjvzZkrBhvQ(OsOMfI4ZOs(UkQAKKi3vv1OrKMgrojc1Zr6AOIZJqwPkkUTahNuvx(Q1hFZujcQd3uCwD1iMBkCGWo2NVAnvAKDkFzl0SPgqEygTjV3hY75BQaGJc9Mi9ky0Q1hF16JVPkgqn6O)(WWdebrXHoMYyrWbWGiiYL8jFF(MQya1GOpSi4ay)qK3763i3xytvmGAquyihPnc0NutvmGAq0htGjfWyJ8LX1pefkjfg2hNMQya1GOpSi4ay)qephV7wFBnvXaQbrFmbMuaJnYxgx)FyrWbW(HOvIZpriIy2YD6vW6JanvXaQrh93hgEGOpMatkGXg5lJRFiko0XuglcoagebrsUKL4qcej5swIdjqKKlzjoKarHsN4L6ZTPkgqni6dlcoa2pe5pT5j72uxHWPU3GR1SPw8Ywym(UU5kb1uaWrr1Q1KqdreEKhaDQwF8nvXaQbrFyrWbW(HioUB95BQIbudI8Ex)g5Anj0q0Q4qPvRp(MQak9sniAPaVt7Z3ufdOge9Tuedwe5FiYh63o52xytvmGA0r)9HHhicIIdDmLnqKRXGiiku6eVejqeBxwUwZ0gNNBNHTRG1Cv8kIxJOMokcoawx3CvCuaWrr1Q1ulEzlmMVRRvR5Ith0BI0RG1NFZV1ubGTdKjMztK7dZUcwx3KG7gPIytfte3uPr2zt4zAQZSeSlB9X3upq8coKhA1Q1mDoyI1Ppph3MoWwkI4XrrGtGboUYxJOUUwTwa
I tried to optimize as much as possible while keeping it to only one button. I hope someone finds these helpful.
Mercurio