How can variant B imply variant A?

[Jeremy Lavergne]

> Independent of all that, my two questions still stand:
> - Is it possible to enable a variant if I'm already too late for

How are you too late for this? I don't see how you can be too late.

> "variant ... requires ..."?
> - Is it possible to use "if port X is installed" inside Y's Portfile?

This is just a bad idea: your package will install differently based on what's available, and not even consistently (e.g. archives). Use subports with the appropriate dependencies.