People are welcome to fork and add their own features. They will need to support and maintain their features just like me. They will need to pull in upstream changes or their fork will rapidly age.
I target Inspeqtor Pro at teams and businesses with a real budget. They want a supported, pre-packaged product that solves their problem. If someone is willing to find and use some other person's fork, they were probably never going to pay for the Pro product in the first place and therefore there's little to no real competition here.
Will you reject pull requests that compete with Pro features?
I'm just wondering how governance of the project works. I assume you're already dealing with the same sort of thing with Sidekiq. I just find this sort of business model interesting since the more common approach seems to be providing hosting or priority support.