There's a common misconception. When an engineer gives an update on mixing, many believe the album is soon to follow. In reality, the mixing phase can be a lengthy one, especially when dealing with a perfectionist. Now, it's not exactly clear who Mike Dean is mixing in his recent studio update, but it's easy to assume that Travis Scott's Astroworld is the project in question. If so, it might explain the seemingly never-ending purgatorial status, as you already know Scott has been keeping his loyal producer busy with all manner of zany sonic landscapes.
Given the layered nature of Travis Scott's music, it wouldn't be surprising for a single song take longer than average, especially if he reverts back to Rodeo's gargantuan run-times. Yet at this point, all things Astroworld are beginning to feel like deja vu. It wasn't long ago that Travis seemed to indicate the album was finished, though it's entirely possible he has since changed his mind about something in the interim. It's equally possible that Dean isn't actually mixing Astroworld at all, but rather another project entirely.
It's possible, given Mike Dean's revered status. Yet all signs post to Astroworld, and his many Instagram followers seem to believe exactly that. For now, it's "MIXMODE" as usual. Let us wait with bated breath.