Hello,
I saw this thread was recently pretty active and agree we're overdue for an update. We can assure you work is being done on this. For those asking for the ability to add a border around the outside of an email - that is planned to be added.
With the addition of that feature, for those of you asking to remove or modify an existing border in a campaign, we just updated this thread requesting that. This new feature will allow for that as well, but we just need to do more work before it's ready to be release. In case it hasn't been relayed yet, there are only certain templates that have the outer border currently that is unable to be changed. If your goal is to remove it, you can select a different template in the meantime.
No firm time frame yet, but we'll keep this thread updated.