It's more likely that Patreon will turn into YouTube than it turn cancerous. They have the creators and they have the eyeballs; there is no need for those creators to be on YT to "reach wider audience" because those freeloaders aren't paying them. If Patreon could become the YT of paid content, it could be huge.

Then again, YT can turn Patreon functionality on in a blink, offer everything for free and then some, offer features to subscribers that Patreon doesn't have, and over time, slowly, erode a big chunk of their users.

Even though Snap has not completely died yet, Instagram was able to suck out their oxygen pretty bad by simply offering a wider audience to the creators. YT can't pull the same trick here, but once they found what works, it's only a matter of time.

It will be interesting at the very least.