You can still play online with 5.5.1, i am still on 5.5.1 and i play splatoon online
If you have haxchii you can still use hacks on 5.5.2, only browser expoit is patched but if you update to 5.5.2 without having haxchii then you can use unstable 5.5.2 browser exploit to install haxchii using DS...