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.
Growth must be continuing otherwise Bitcoin can be considered as a dead coin. Right now, there are some big issues that Bitcoin developers should be facing to help this cryptocurrency stay on the game for a long, long time servicing as many people or users as possible. Reading along this forum, we can be aware of the many challenges that need to be addressed as soon as possible. Innovations, changes for the better are all part of Bitcoin and we should be expecting them. As a man-made invention, Bitcoin is never perfect and will never be that is why development must be ongoing and will never stop anytime.