This doesn’t help at all.
Beeminder is supposed to be a tool that helps you accomplish your goals. You’re supposed to be able to say “I created a goal, and now I know that either 1) I’ll do the goal or 2) I’ll get stung”. Your suggestion makes it possible for neither to happen. The hypothetical extreme version of this is that Beeminder never helps you do anything and is completely useless. Sure, not getting charged money makes it “fair”, but the Internet is full of useless things I don’t pay for.
You might say it’s not that likely that a goal would repeatedly fall into the problem of derailing on the weekend, or that it’s “close enough”, but Beeminder is always talking about bright lines being critically important. They taught me that philosophy, and I subscribed to it, but now they have to live up to it. If Beeminder can’t actually give me a guarantee re: 1) or 2) above, then I can’t use it effectively.
It’s icing on the outrage cake that these are premium features. Putting buggy stuff behind a paywall is not a great recipe for success IMHO.