In his post on Medium, Liu stated that the goal of Pokevision was not to “cheat”, but rather to address some of the problems the game had at the start. Given that Pokemon GO is still relatively new, teething problems are to be expected, and Pokevision was created with the intent to help fill those gaps until Niantic could get up to speed.
Liu even stated that there were plans to shut down the service once Niantic addressed said problems, but the fact that it took longer than expected meant that Pokevision had to stay alive a little longer. As we waited more than 2 and a half weeks, the tracker was still not fixed. “We noticed more and more of our friends leave the game; the only way I — and I know experiences vary here — could convince them to play was show them Pokevision, and say that ‘Hey, here’s a temporary remedy to the tracking issue — we’re still optimistic that Pokemon Go’s tracker will be fixed soon!’”
From what we can tell, Liu does not seem to want Niantic to allow Pokevision to come back, but rather he seems to be appealing to the developers to fix the game and let it reach the potential they know it will. You can read his letter in full on Medium.