Unless they were mining for spending on microtransactions. But Bitcoin's PoW hash is too favorable to ASICs versus CPUs to make this viable as you say only a few satoshis in relative hashrate.
I designed Cuckoo Cycle to be a low-power PoW that spends the majority of runtime waiting
for random memory access latency (almost like Proof-of-Wait).
https://github.com/tromp/cuckoo offers several bounties for disproving its claims of being an ideal memory bound PoW.
It could easily run on smartphones while they charge overnight, with no fear of overheating.
The more people are able to mine (including botnets that will still be vastly outnumbered) and willing to do so at a loss, the less commercial mining can survive.
Bitcoin would have to introduce an alternative PoW very slowly;
p*CPU + (1-p)*ASIC where p rises from 0 to 1 (or 0.5) over many years.