The BM1387 ASIC chip is capable of ca 0.07 TH/s and consumes roughly 5 watts.
You would need some 70 millions of those installed to match the current total network hash rate. No need for billions or users.
Honestly, I don't know why you have refused to listen to my comments on this. No phone or laptop will ever be able to support this. The power consumption is way too high. Less than an hour of mining and your battery will be drained.
Phone and PC/laptop manufacturers could add an ASIC to their boards for example.
Or dongles could be made (possibly combining OTP generation with mining killing two birds with one stone...).
Quite honestly the "price" to pay (ie device + energy costs) is well worth it !
What do you think ASIC chips are? LEGOS? Do you seriously think that anyone can smack a big ASIC chip into a device with a LOW TDP design in mind? The price for the design could very well cost more than several HUNDRED thousands and the phone would each cost more than $100 extra and not everyone would use it. Honestly, no one would buy it.
I believe that the major issue would be rather on the network bandwidth / latency side of things.
I do not know if bitcoin has been designed with such a heavily decentralized mining in mind.
Its not. Why the hell would it be? Decentralised mining will NEVER be realistic.