TwitterDev finally announced some more details.
1. Delay new rules for 4 days.
2. Free "bot" level of up to 1,500 Tweets/month for a single authenticated user (probably no read access).
3. $100/month "low level of API usage" tier.
4. Premium API (the expensive one that had prices listed) goes away in favor of Enterprise (the even more expensive one with no prices listed).

Before anyone asks, this does not mean 3rd party clients are coming back, if anything its the exact opposite.