When it is out of beta, will it be still free? I think I should try something more lightweight than GitKraken, it hangs up more and more often.
Fork might become paid but not in the near future.
It accomplishes a few things - measures interest, give people that value the product a way to thank the creator, and adds a FOMO factor which can be good for publicity, if he wants it.
When Google Reader shutdown, Feedly offered 5000 lifetime subscriptions for ~$100 (vs $65/year). They sold out in 8 hours. It's not the same case, I understand - but the idea is similar.