I am in favor of 5Es open Beta. This is because its clear from the release of 4E the designers/play testers were playing a different game from the one released which lead to tons of errata and the obsoleting of the first books released in just a few months. An open beta will stop that type of thing as well as a number of other problems 4E was plagued with.
However, when I worked at a game company I was not in favor of open betas (except for networking tests or marketing reasons) because you often have the tail wagging the dog. I am deeply skeptical that WotC realizes that only a small portion of players and DMs are responding to their surveys and these respondents may not closely represent the whole of the people that play D&D.
That being the case, I encourage you all to respond to the blog surveys and make sure your opinions are heard.
Just go to the Playtest link here: https://www.wizards.com/dnd/DnDNext.aspx
And go through the Related Articles on the bottom right. Most have a few survey questions for you to vote on.