Items not allowing root topic

I have searched and been unable to find answers, least ones that account for changes over time. So if I have overlooked the obvious then my apologies.

I am looking to upgrade to a m7, hopefully as soon as tomorrow. Being able to root is not negotiable. So what I am wanting to know, are there any set of circumstances which would render a device unable to be rooted? I have no issue with requirements of downgrading firmware, or anything such as that, wouldn't be the first time. Simply want to ensure that nothing exists which can't be worked around.
Thanks

[Q] Transferring items Fire HD 6 topic

I am on windows 7 and for some reason I can not drag and drop a file into my Fire HD 6. It also says the driver is not installed correctly but I can still view the internal storage on it. I have looked for a solution but have found nothing. Any help would be appreciated. I wish they made Androids less complicated...