Unless a manufacturer that makes the cameras or lenses being adapted creates the adapter, it would be highly unlikely that the adapter would ever offer AF.

That is, if Sony makes an adapter for Sony A mount lenses for their mirrorless cameras, you can be your last dollar it will have AF capability.
And this they already do.
It would be the same for Sigma, if they made an adapter for their lenses for one mount type being adapted to a different mount type.
They already have the AF knowledge of one mount type, if they had the knowledge of the adapted camera type too .. then the interface should be easy to achieve for them.
it would still involve a cost component and as such the adapter with AF ability would be more expensive than one with no AF ability.

I dare say that it's unlikely that any company will ever create an AF capable adapter for one mount type lens to fit another mount type camera body.
But this doesn't mean that it will never happen.

I reckon Yongnuo may one day do this. They have recently made a Canon 50mm f/1.8 lens similar to the Canon lens of the same type. Now that they have some AF capability, and if they ever produce an AF capable lens for say a Fuji X mount, or Sony E/FE mount(as examples) then they have the knowledge of the AF systems for the individual manufacturers products.
Translating those AF capabilities from one to another(within reason) should be possible too.

Of course there will be some lenses that just wouldn't be practical to adapt one AF type to another .. such as Nikon AF-D type lenses(which require a mechanical AF motor external to the lens). Such a lens would be difficult if not impossible to drive automatically by a camera with electrical AF drive.

FWIW tho, Sigma do offer a mount conversion service to a limited range of their lenses. I'm not 100% sure which lenses and which mount types can be converted tho.

As it stands tho .. yes you can get an adapter fo almost any lens of a particular mount type(eg, Canon) to fit almost any camera of a particular mount type(eg. Fuji).
There are limits tho due to the backfpcus distance of the lens tho. No adapter will allow AF as of yet.