Charles Rampant
Adventurer
Given the way that nostalgia and embracing D&D's weird past seems to appeal to the current team, perhaps they'll surprise us all and do a Spelljammer article?
More seriously, I'm not sure yet whether the column is truly just beta-tests for books - some of it making it into a book doesn't necessarily make that its purpose. The column is obviously going to have 'excite people' as one of its main design goals, but beyond that is perhaps hard to guess. Probably clerical domains are something that we can expect, though: we all know that we could do with more of them, and their shape and size would easily allow a half-dozen with a few new spells to take up a whole column.

More seriously, I'm not sure yet whether the column is truly just beta-tests for books - some of it making it into a book doesn't necessarily make that its purpose. The column is obviously going to have 'excite people' as one of its main design goals, but beyond that is perhaps hard to guess. Probably clerical domains are something that we can expect, though: we all know that we could do with more of them, and their shape and size would easily allow a half-dozen with a few new spells to take up a whole column.