Author here! Really glad to have sparked a lively discussion in the comments. Since there is so many threads since I last looked at this post, making one top level comment to provide some thoughts:

1) I agree that estimating a bug's complexity upfront is an error prone process. This is exactly why I say in the post that we encourage everyone to "feel out" non trivial issues and if it feels like the scope is expanding too much (after a few hours of investigation), to just pick something else after writing up their findings on the bug.

2) I use the word "bug" to refer to more traditional bugs ("X is wrong in product") but also feature requests ("I wish X feature worked differently"). This is just a companyism that maybe I should have called out in the post!

3) There's definitely a risk the fixit week turns into just "let's wait to fix bugs until that week". This is why our fixits are especially for small bugs which won't be fixed otherwise - it's not a replacement for technical hygiene (i.e. refactoring code, removing dead code, improving abstractions) nor a replacement for fixing big/important issues in a timely manner.

Very interesting post, thank you!

I'd also be curious to know the following: how many new errors or regressions were caused by the bug fixes?