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I'm quite interested in supporting additional databases, particularly big names like Oracle and SQL Server. For SQL databases, the MySQL adapter is probably the best starting point. Before starting on an adapter, check the issue tracker to see if there's already a work in progress, and feel free to open an issue if there's not one.
For interop adapters (e.g., Heroku, Ruby on Rails, etc.), I generally feel those should live in separate plugins, unless you can name a good reason to the contrary.
I'm open to a richer feature set, but that means starting from the ground up, not blindly copying dbext. Let's start by figuring out useful abstractions before we map every variant of querying the table under the cursor.