In regards to tiers, you can check out this thread for more info. But for a very recent update, check out the last section – What’s next? – in Ghost’s blog post announcing v4. Spoiler: it looks like they’re gonna be called custom plans rather than tiers.
Also very excited for this feature. We’ve been migrating from Patreon, but we’ve been hesitant because we’ll lose subscribers at the higher tiers. We’ve got patrons that have opted to donate at higher levels, some even custom, and of course if they come over now, they’ll have to come in at the lowest level. Ghost is an incredible platform, and very enticing for many, but once it comes out, the tier (or “custom plans”) feature will make it a no brainer for those considering the switch. Hope it’s soon!