Can you give some more information about why you feel it has the neutral image you're referring to that would apply to sleep in? My experience has been that it is usually negative.
For instance, as in this explanation from a vocabulary website
「寝坊」という言葉は、朝起きる時間に遅れてしまうことを指します。
具体的には、アラームや時計が鳴っているにも関わらず、寝ぼけてそのまま寝てしまったり、眠りが深くて起きることができなかったりすることを指します。
寝坊は、学校や仕事、予定などで決まった時間に起きる必要がある場面で起こることが多く、そのため遅刻や予定の変更が生じることがあります。
That's not to say I'm denying a more neutral use is possible, but it would be helpful to have a source that says that's what the meaning is.
If you do a Google image search on 寝坊, every image is someone waking up and freaking out when they see what time it is.
@avancerat Even if "sleep in" could have neutral or non-negative connotations in English, it does not mean that it is a good translation for 寝坊. Unless there are credible Japanese sources that indicate that 寝坊 is anything but negative I do not think "sleep in" should be added as a translation.
Regardless, this word is defined in the JMdict project, so if you have comments on how a word should be defined you can hover over "Links" on most words, and then click on "Edit in JMdict" to be taken to their editing interface.
Suggestion - add "to sleep in" to 寝坊(する)
I want to preface this by saying that I have no real sources for this claim outside of personal experience, so there's obviously a chance that what I'm about to say is not correct.
I think the entry for 寝坊 should include "to sleep in".
It currently has:
1. sleeping in late; oversleeping
2. late riser; sleepyhead
As you can see, all of them have a rather negative connotation.
Sleeping in, as in sleeping longer than what you usually do, doesn't necessarily have to be a negative thing. It could, for example, be a form of recovery (which is a good thing).
Therefore I think it would make sense to add "to sleep in" as an alternative translation for 寝坊.
(https://dictionary.cambridge.org/dictionary/english/sleep-in)