You're probably safe but...
There is a danger. This is why the default
python on the command line is still python 2 for many distributions.
Will this actually hurt you?
That's impossible to know without knowing which linux distribution you have which packages. I doubt anyone has full oversight of every package available in the world to know what would break if you tried this.
However as time goes on the danger gets less. Python 3 is maturing and those still using python 2 are much more aware of the danger meaning they can protect against it. At this time the danger might be low enough for you to get away with this.
What's the danger?
There are many programs that run on linux which are written in python. You may not have realized you're using python because you invoke them as executable. They use the shebang to invoke python without you explicitly calling it.
The problem was that very many programs were written for python 2, who's shebang was set to
#!/usr/bin/python. Likewise shell scripts calling puthon scripts were prone to simply call
python script.py. If you changed
/usr/bin/python to Python 3 then many programs would break. However as time goes by, most older programs have been modified to request a specific version (
/usr/bin/python2 or even
/usr/bin/python2.7). Python 3 programs have been forced to specify a version due to the statuesque.
Check before you change
I wouldn't change this on a production server unless you have a really really good reason. However if you're changing your own laptop the risk should be much lower.
I would try running this to be sure:
grep /usr/bin/python /usr/bin/* /usr/sbin/* 2> /dev/null
... look for anything calling
/usr/bin/python without specifying a version. If there's nothing there then go ahead and try. Just be on the look out for things breaking unexpectedly.