Alternate Ways of Contacting Customer Support
In reality, in order for anything to possibly be seen by Developers (the people you would want to give the feedback to) it would be to post it on the General Forum fir a CM to forward on to them. There is no other way to contact them. Blizzard closed out most of their external email addresses a year or two ago, and even recently got rid of at least one more.
I'm not suggesting you give details here, but if you give us a vague idea of what it is in regards to, we may be able to point you somewhere else, but it's honestly not very likely.
Your best option, to my knowledge, is to post it in the most appropriate forum. For instance, if you had a suggestion about a Dungeon, you could post your suggestion in the "Dungeons, Raids, and Scenarios" forum.
Posting constructively is the best means of getting your post heard. Explain clearly, but concisely what your issue is, without hyperbole. Why you think it's a good/bad thing, and what suggestion you have to change it. Also, remember that generally Blizzard is much more interested in the discussion of the player base, rather than individual suggestions. You'll be posting on an open forum, so expect responses. Some will agree with you, some won't. Some will be civil about it, some will not be. Ignore those that aren't civil, and respect dissenting opinions.
Please report any Code of Conduct violations, including:
Threats of violence. We take these seriously and will alert the proper authorities.
Posts containing personal information about other players. This includes physical addresses, e-mail addresses, phone numbers, and inappropriate photos and/or videos.
Harassing or discriminatory language. This will not be tolerated.