You re right that Arsenal were not in the list of top 4 contenders in season beginning but now, they are there.
If Arsenal can maintain their winning streak then I'm sure they will qualify for the Champions League next season. The Premier League has become increasingly tense so far as the race for the title and the race for tickets to the Champions League next season looks increasingly exciting. Manchester City are also not as secure as before at the top of the table as Liverpool managed to stick tight behind them with 3 points.
I actually think that Manchester United is endangered, because they have played 26 matches and have 46 points and they are in the fourth position. Right behind them is Arsenal who has 45 points and they have played 24 matches.
So. I think if Arsenal can continue winning they will surely go past Manchester United in the points table and if Manchester United wants to stay in the 4th position they better not drop even a single point and also pray that Arsenal loses.
Liverpool also got dangerously close to Manchester City and Only three points behind right now from Manchester City. so it is going to be really interesting How the league table will Shape Up in the future.