Dallas are a wing player short of making full use of Marion's ability to play the four.
I'd love to see them trade Jason Terry for a quality wing player who can become their new sixth man. Develop a nice eight man rotation with Haywood + wing + Beaubois off the bench behind their current starting lineup. I think that would give them better lineup flexibility and more defensive quality.
Agreed, Marion at the 4 and Dirk at the 5 makes a lot of sense for the future in Dallas.
I think Marion gives them three main lineups
(1) Big physical defensive lineup -- Marion at the three alongside two seven footers + Kidd + either a PG or wing
(2) A quick transition + defensive lineup -- Marion at the four alongside a shot blocker at the five
(3) An offensive lineup -- Marion at the four alongside Dirk likely with Terry, Kidd and Butler too
I think all three of those lineups are excellent. The first one is particularly useful against high scoring wing players like Kobe Bryant. The second one will make a terrific backbone to a second unit. And the third unit is an explosive offensive unit, a good finishing unit.
All three lineups pose opposing teams radically different problems. It allows Dallas to create or take away matchup problems against just about everyone.
All are capable of being game-changing lineups.