On my mind, it will be very useful for beginners if we will integrate this
in core of Rails.
What do you think about this guys?
We definitely like the way controllers are idiomatically written today.
An ivar is not bad per se, a filter is not bad per se. What you list as
disadvanges are not categorically good or bad practices, their particular
application in some problem or another may be.
In Rails, controllers communicate with views using ivars, it's fine.
Idiomatically they set the subject of some actions using filters to reuse
the query. It's fine.
Of course, it is also fine that your apps use your preferred style.