You are not going to see an Atom on 7nm from Intel until sometime in the 2020s. The next Atom, known as Gemini Lake, is still on 14nm (probably 14nm+). Then you will likely see three gens on 10nm (10nm, 10nm+, 10nm++). So expect that 7nm Atom MAYBE in late 2021 if all goes as planned.
My guess is that the CPU core will remain the same but they will do the same trick that they did with Kaby Lake vs Skylake -- improve the transistors, optimize the physical design, and include Gen10 GPU.
This should allow for higher all-core performance (leaked benches show that it does well with one core loaded but throttles back significantly in 4-core loads) as well as better single-core performance. The new GPU should make it more appealing for low-cost personal computers, which will be the prime targets for Atom-based SoCs.
The places where Atom could conceivably compete with ARM A72/A73 is in the micro-server and low-end networking SoC market, but the former hasn't really taken off as customers seem to prefer higher end/more powerful Core CPUs rather than many-core Atom processors.
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