I just got approved here, but have been on Mastodon for a couple of months. Mastodon signup was a lot glitzier, and yet I still couldn't convert my friend, who was like "I don't understand, what do you mean it's like email? >_<". I don't have high hope for Lemmy atm...

I think Reddit will backpedal and renegotiate with users/devs down the line, once the initial backlash has died down, and they have lowered everyone's threshold of what they would consider a "victory". Things like Lemmy will act as a sword of Damocles/safe harbour for the next time they screw up, sure, and that's a good thing. But I doubt Lemmy will explode in popularity, even if some 3rd party Reddit clients are discussing adding Lemmy support to sort of rugpull Reddit, and that's for 3 reasons(imo):

1. The hosting costs will be exorbitant for all those new users, considering
2. Lemmy will be stuck in the exact same boat as Reddit re:all those unpaying users, except now there's no ads either. Donations are the honourable business model, but a couple thousand well-meaning people with disposable income can't properly finance a popular platform.
3. Even if the Lemmy community solves the above 2 problems, you still have the deciding moment of the "let's jump ship today" user tidal wave, which will make or break such a migration happening. Closest thing I can think of is the WhatsApp Privacy Policy shenanigans in '21. Melon Husk said "Use Signal" - a fine suggestion, tbh - but Signal wasn't ready for this, and so their servers crashed and burned during the tidal wave, while for-profit Telegram just paid for more servers and thus converted the refugees into users.