What’s wrong with this? It looks grammatically correct to me…
"Unfortunately, we won't be renewing our contract with you"
or
"We regret to inform you that we will be going with another candidate"
Changing those to the simple future makes them sound much harsher to my ears, so I would venture that the progressive is a mechanism for softening the impact.
This is answered in the next sentence of the article: it’s “support” not “be supporting,” Microsoft.
The is using the future continuous when the simple future is more appropriate to the message.
That said, "will no longer support" is more succinct and clear enough.
That's not an answer to "What's wrong with this?", that's the author's preferred wording.
Both the future and simple versions are appropriate, whereas the author makes it a point to highlight their preference.
And of course here we are, poking it further.
(1) You are responding to a quote about a proposed rewrite of the sentence which would be clearly wrong independent of whether the quoted text was (the “less correct” was chosen because the proposal asked if it would be “more correct”), and
(2) No, there's no such requirement for the use of “[sic]”; use for things which are not strictly incorrect but not comport to a stylistic preference of the author presenting the quote (or one that the author expects the audience to have) is common. For instance, Google's dictionary's usage example for it is “a story must hold a child's interest and “enrich his [sic] life.” What the “[sic]” flags is grammatically correct, though recently usually stylistically not-preferred.
“e-books that use the .epub file extension, Microsoft Edge will no longer support”