As subject goes, is Bitcoin the maximum version?
Is it still possible to develop it?
You may want to spend a little more time reading about Bitcoin. It's still in active development, and will continue to be for the foreseeable future. There are still a few glaring issues that are yet to be addressed.
Can we still expect better coin than Bitcoin?
Of course. The possibility will always be there, it's the probability that is in question.
Of course, it's in active development, but perhaps the op wanted to say (or could agree it would now be more interesting to discuss) whether any huge change is coming. Small improvements are good, but how much can we expect Bitcoin to change? How much is it even possible to change it? What is based on consensus and what definitely stays the same? And speaking of consensus, how likely is it that consensus would be reached about a very major change (some people called for Bitcoin to become PoS, for example)? Does Bitcoin even need those changes? I believe if there's something that can be done with scalability, it should be done, but apart from that I'm fine with small changes.