tl;dr version: 1. Ai hiding is bad for the platform in the medium term. 2. I believe there are some relatively simple means --more transparency-- to keep it in check.
Here are full details.
1. How do you want a CG competition to look like? My take is this:
The good players will find incredibly overpowering tactics and patterns. As they play the game more, they'll be forced to find counters to those tactics. The majority of tactics that at first appear unbeatable end up having counters, though they are often difficult to discover. The counter tactic prevents the first player from doing the tactic, but the first player can then use a counter to the counter. The second player is now afraid to use the counter and they're again vulnerable to the original overpowering tactic.
(Accidentally, this is a quote from Playing to win). I think this strategy evolution, often discussed in the chat, is what makes CG different from many other competitive programming platforms. But if, say, 30 best players keep hiding, this scenario will fade away. We'll see fewer improvements during the week, less excitation etc. The unfairness coming from asymmetrical tests setting was already mentioned. These are real problems.
Yet, hiding is at present arguably the best tactic (and 100% valid too).
2. So can we do something smart about it? My first attempt above was admittedly lame... Here is another take:
In higher leagues, every bot that gets to top 20, has his 100 battles archived and easy to see for others (enough to keep the best bot for each top20 player). Also, this bot's code should be easily reachable for others to test in the IDE. We make a clear rule that intentional (esp. time-based) crippling your bot on the display/arena is forbidden. Once you've tested, you stay there, that's only fair play. Finalists (top 3 or 10, say) can be more closely examined at the end as in The Accountant.
People not pushing to the arena at all are already kept in check by the risk that the solitary tests in the IDE don't guarantee much for the arena behavior. Additionally, we could restrict the IDE testing to no more than N adversaries per hour (N to be determined so that pushing to the arena from time to time would be simply the best option for everyone; consequently, during a contest, Spunk should be restricted too).