I think answers for questions that are "on hold" can be sent as private messages to the users' inbox by 'highly experienced users' like moderators or others with high rep, thereby eliminating the need for discussion and still maintaining the standards. It will also maintain privacy. This can be done especially for users who have less than 6 months of experience at SE. This is probably the best way which still fits into SE.
Well, no. Because that's not what Stack Overflow/Exchange wants to be. They don't want to be a site where questions are privately answered. The primary purpose is not to answer the OP's questions. It's to create a quality repository of questions and answers, useful for the wider audience of the internet. That the OP is helped as a result of that is, to some extent, a nice side-effect.
Private messaging has been rejected many times. Private answers wouldn't be any better. If it's not good enough to be public, it simply doesn't belong on the site.
Interesting thought, but I rather disagree with it.
Almost everything you do on Stack Exchange is done in public. This is deliberate; Stack Exchange was built to make a public store of knowledge, and private messages don't add to that. (Also, private messages make it easier for people to misbehave).
When a question is "on hold", we can still comment on it. In this way, the suggestions given to the OP can be read by everyone, and others can expand on the suggestions given.
I can think of three reasons one might want to implement this:
The poster still gets the answer even though it should be closed.
If we did this, what would the point of closing a question be? Why stop posting terrible quesitions when you'll still get an answer? At the end of the day, (most) people who ask those kinds of questions repeatedly just want the answer and don't care about downvotes or rep
It "warms up" newbies to the site
This kind of goes back to the first point. Why conform to the standards of a new community when you can just get what you want with a slight slap on the wrist? Even if the forgiveness was removed after a while, we'd have this same problem at that point. Besides, there's already a ton of stuff for new users to look at.
The answers could still be useful to other people.
This is more of a grey area and has been discussed at length. While there is some validity to this claim, more often than not, a question that is closed has a good reason to be. Dup's are linked, off topic's can be migrated and spam is mercilessly terminated. If there really is a good reason to open it, you could always flag your case or bring it to meta for discussion.
[…] eliminating the need for discussion and still maintaining the standards.
High quality standards on SE sites are maintained specifically by vetting the answers in public. This peer review process centered around voting but also including public commentary is essential to the function of the system. Bypassing it would ruin the entire model.
Instead of destroying this working model, perhaps you should find (or start) a service of your own built around the idea of private answers. I think you will find experts are less interested in participating than you might hope. Perhaps your model would include some other form of incentive, but it doesn't mix and match well with the SE model.