Maokai top??

you don't watch the LCS much, do you?

If I had to list his strengths,

1. Sustain on his passive gives him good trading power and keeps him in lane.
2. His CC, particularly his Twisted Advance, makes him extremely good at gank assist.
3. His Ult makes him a team fighting monster.

Just keep in mind that you probably won't be able to carry as Maokai, and will need to rely on your carries to win the game. (the biggest YoloQ problem) And that you play for the team fight. Get tanky, engage with twisted advance, Ult, and watch the mayhem ensue.

Yeah its viable but you don't do damage come late game, which leaves you at the hands of a hopefully competent midlaner or an ADC who would hopefully know how to kite. It's your call, just know that you won't do damage after you finish ROA.