Depending on the games are setting, I would think the 3570k is getting its end of life.
I know it's overclocked but more and more games want cores instead of faster single cores. I don't see the 3570k lasting 3more years... Depending on the games you play
You could drop and i7 or exin in and extend its life a little..
Definitely depends on the games you play. I don't play very demanding games, still mainly quake live, quake champs, planetside 2, apex legends etc I never really get around to playing AAA games until years after they're released.
I may upgrade to the next zen chips if they can match 8700/9700k IPC levels. Or as you say drop in a i7 for a few more years, what would be a good cheapish upgrade ? 6700K ? seen a few of those. editnvm , seen 6700K needs ddr4.