At least one demonstrable difference I can see between your recollection and this feature is that the column name being part of the DDL pushes the logic down into the DDL, versus every client having to carry that magic expression around with them. I think it's likely the age-old application-logic-client-side versus stored-proc camps
db=# select id, cast(length(name) AS text)||'0' as silly from my_table
But if a function called silly with input type my_table existed, you could still do your second query. It has syntactic sugar for making a bare function name implicitly invoke on the current row record.
I can't remember if that sugar could also be used in an expression index. I never really used this syntactic feature, as I thought being more explicit with function calls would be better coding style.
Can’t wait!
You can, and probably should, do these things in your application code. I mean, it's not really that hard to make a string lowercase, you don't need to define a "virtual colum" for that...