I doubt that he has long-term plans for dogecoin. He is just trolling and hyping with it. But people has created a cult of Elon Musk the dogecoin saver and worship it. Again, people are responsible that dogecoin price went up when Musk mentioned it in his tweets, not he pushed price up on purpose. I cant understand why people call him dogecoin saver? Community are the ones who pushed price up, Elon did not invest or trade to pump dogecoin price up.
Just a regular influencer. Regular but very wealthy and able to allow losses. He has never been a crypto saver, it was just profitable for him to act in a particular way. If it will be profitable to make anti-bitcoin tweets, no doubt that he would do it.
However, Elon Musk is in a trap of his reputation. No matter what he does, people praise it. If one day he will say that white is black, some people will start to doubt if isnt white really black. If he will say that eating is unhealthy, there will be casualties around the world.