Make Ignite scale with 2% missing health per tick, but reduce the base damage a little bit.

No.

This would be terrible with the fact that it also reduces how much healing you receive, so you're basically guaranteed a kill.

I honestly don't see a reason to change Ignite.

lol no, I hate ignite as a spell, it makes lane bullies unbearable since many of them can 75-0 you at level 3 if they have ignite (looking at you ) and you can't heal through their burst. The only reason i'm fine with it remaining right now is because you need GW to deal with certain champions and not everyone can build

I disagree, but because just saying no isn't useful I'll give some reasons. I feel that currently ignite has it's uses as a summoner spell, it is not too strong nor too weak, and tinkering with stuff that isn't broken is usually not advisable. While that isn't a good enough reason on its own, you have to keep in mind that currently ignite is used at least in part as a counter against heavy healing champions like etc. where you might not want %missing health burn but the current effect instead, as well as an anti-healing spell in general (f.ex. if you the enemy has lifesteal, a fiora or a soraka). Another reason is that the % missing health would not affect all champions equally (depending on your pov) because tanky/high health champions would be hit harder by it.

I'd rather it be changed to give %current hp so people are rewarded more for committing to a fight with ignite more rather than just saving it's obvious they can use it to get the last few hp of a fleeing enemy.

Right now the only benefit to igniting early is the healing reduction which isn't all that relevant against many champions.