I think questions about future series should be categorized as off-topic.
One cannot absolutely base an answer off of time since the series ended. For example, it is possible a series with a large fanbase could have an addition series release 7/8 years later.
One could estimate an answer basing off the content left to cover if the show is based off a manga/light novel, such as Sword Art Online and perhaps with a combination of ratings and popularity thrown in. However, no-one apart from the people involved in the process is going to know much.
Often details of future events can be rumours or there can be cancellations, so answers can be based off of volatile information.
The problem is that there are some questions that ARE answerable, that we will miss out on if we close all these questions. But I think the benefits of these few questions being answered are highly outweighted by lots of unanswerable or volatile questions.
I suggest, much like @GraceNote's post on What do we do with questions about future events/releases? back in '12, that we leave future events to new sources such as ANN or Crunchyroll.