I have a question that is intended to allow Unicode input. No-one has posted an answer yet but someone has asked if it can be ASCII input only. That could drastically change which languages were competitive. Can I have the same challenge but score ASCII-only against ASCII-only and Unicode against Unicode? I.e. make them non-competitive against the other type, only with their own type?
Allow more than one category of competition in a single challenge
The general consensus on CGCC seems to be that limiting a challenge to a subset of languages is bad. So a language such as GolfScript, which has no built-in UTF-8 support, should not be forbidden from taking part in challenges such as this one.
On the other hand, an answer that can only handle ASCII shouldn't be considered to be directly competing against answers that handle full UTF-8, UTF-16, or UCS-4/UTF-32. Allowing more than one category of competition is a really good solution to this dilemma.
For that matter, another type of split competition that should be allowed is Arbitrary-precision answers vs. Floating-point/Limited-precision answers, but that's a topic for a another Meta post.
By holding two different competitions in one challenge, your challenge becomes unclear, as all questions require one specific scoring system that leads to one specific winner.