Is splitting a challenge into multiple categories a good way to have an optional difficulty without bonuses?

Question

Sometimes, in a challenge you might want to create some variations. You might want to encourage some extra constraint or limitation, but don't want to obligate everyone to attempt the extra difficulty, especially if you want to encourage using esolangs. The versions may still be too similar to post separately.

Normally, you'd solve this using a bonus. You say: If you meet this extra requirement, subtract X from your byte count. This is, however, discouraged. It's really hard to balance a bonus, either it's so overpowered that everyone needs to use it to be competitive or so useless nobody will.

What if, instead, you just state in a challenge that any submissions meeting requirement A do not compete against submissions that don't. That way, everyone is completely free to choose if they want to try either variant, no matter if it's "worth it" for a fixed bonus.

Some examples of possible extra challenges:

• Less restrictions on input, for example all Unicode for the harder version vs ASCII only for the easy version
• Not assuming a solution exists
• Restricted complexity, in a challenge where brute force and efficient solutions are both possible
• Not using specific builtins

This is specifically about posting a single challenge where I mention both variants count as a separate category. Would something like this be appreciated or are there some problems I'm not seeing?

Answer 1

Yes, this is fine*

We have a policy that self-imposed restrictions do not invalidate an answer. So, an answer to "Print the \$n\$th prime" that chooses not to use any prime related builtins is entirely valid (so long as they make it clear they're using that restriction).

So, answers that complete the challenge, but with the added restriction of

• a specific time complexity
• not assuming a solution exists
• not using specific builtins

are completely fine - even if the restriction originated in the challenge, rather than being "self"-imposed. So, there is no problem with including optional "bonus" tasks in your challenge, encouraging some self-imposed restrictions that people can choose to follow.

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*However, such answers also have to complete the core challenge as written. If the category changes the original challenge enough such that an answer that follows that category fails to complete the main challenge, then answers will be invalid. For example, if the challenge is

Print the \$n\$th Fibonacci number

and you add in the extra challenge

Print every other Fibonnaci number

This would not be okay, as answers that complete the category are not valid answers to the challenge itself. Additionally, make sure to keep the objectivity of the extra challenges as much as possible. Not necessarily to the same degree as for scoring ("Must finish in a minute on your laptop" is fine), but "make it elegant" would not be okay.