What if wriggles lantern and feral flare granted no bonus damage or gold on jungle monsters?

Then rushing it would make you have very low clear speed and you'd never get it stacked, so you wouldn't want to rush it.

HOWEVER

You could still be "stacking it" as long as you have a machete, an item that any jungler starts with. Remember, that any mob kills you get while holding machete count towards the flare.

So what would you build?

You'd build stuff that makes you clear fast of course.

"How does that make a feral flare jungler different than a spirit item jungler?"

A spirit item jungler can upgrade machete early on and get a bunch of useful stats right off the bat, including safety and sustain and gold generation in the jungle.

If you upgrade your machete to a spirit item, you lose all your "hidden stacks" so a feral flare jungler would want to build something that still gives him clear speed and sustain, but he wouldn't be able to build anything that would grant him as much clear or sustain and a spirit item. In other words, banking all your bucks on flare is risky and that risk is a trade off for its value once finally transformed.

You also wouldn't expect to see flare junglers outleveling and outfarming their laning counterparts because they wouldn't have near the clear speed as they do now, since it won't amplify damage or gold on mobs. The reward of the feral flare path with this change isn't the clear speed or the bonus gold-- it is purely the item itself.

How could that much risk be worth just having some bonus magic damage and on hit healing, now that the bonus gold and clear speed is gone?

It probably wouldn't be with the numbers it has now. I'd buff it a little bit but after it transforms I'd "turn off" the ability for flare to gain stacks by farming the jungle mobs, and instead force the flare holder to fight with his team for assists and kills in order to gain further stacks.

Given the disparity between this idea and what feral flare currently is, there would have to be huge numerical differences between the items of course.