Top lane ignite is viable
At least in lower elos,
Taking ignite can really prevent you from being a sitting duck, only waiting for the enemy jungler to camp the shit out of you, and losing 50 CS before laning phase is over because the enemy is 
Champions that can snowball off ignite really well:

And champions that do not rely too much on teleport for map pressure/ splitpushing:

Ignite becomes less useful around mid-late game when objectives become increasingly more significant, but hopefully you've snowballed enough/ managed not to fall off too hard
Have fun on the rift!