> Rereading, I think you might actually be talking about the use of
> blockchains for real work.  Sorry for misinterpreting.  Sounds helpful to
> do that.  Which chains have workable smart contract systems?  I hear
> ethereum is too expensive for a lot of tasks.
>
Mining of altcoins that do not have their own blockchain can be
implemented in several ways. You can do a sharding, something like a
lightning network. But it all depends on what the production of altcoins
and their cost will be built on.