I used to advocate for more flexes/fewer required RB/WR slots, but it's been my experience that the more flexible lineups tend to reduce league trading as well.
I had not thought of how more flexible roster spots might affect trades. Thanks.
An interesting article I read on rotoworld (link below) mentioned how just adding additional roster spots for a position would increase the value/need for that position.
I was thinking, in addition to what is in original post, that we might eliminate the kicker position and replace it with some sort of flex.