The Sixers have a ton of holes, but let's look at their top 3 -- with the future in mind.
Mr. Isolation
Most good teams have at least one or two players they can isolate at the end of quarters or games, when a score is absolutely necessary. Teams with these players can feel confident in at least one of the following occurring: a high percentage shot, a score, or free throws. Most of the time the player who fills this role is a superstar, but doesn't necessarily have to be.
Possible candidates in draft: John Wall, Evan Turner, Donatas Motiejunas, James Anderson
Possible candidates on team: Lou Williams
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Dalembert Replacement
Samuel Dalembert's much-aligned contract finally expiries next summer, and although there's a possibility he re-signs with the Sixers for less -- much less money -- I'd put my money on this being his last year as a Sixer. Dalembert will be 30 next off-season and it's hard to imagine he'll play at a high level for much longer since he relies more on his athleticism than fundamentals or basketball IQ. (Wait, Sam Dalembert plays at a high level? Yes, Sammy has quietly developed into one of the best rebounders in the NBA and an above average post defender.) Even if Sammy does re-sign, the Sixers aren't contending anytime soon, so a long-term replacement is necessary. Basically someone who can anchor the middle of the defense and grow with the perimeter defenders already in place (Jrue, Andre, and hopefully Wall, Wes, Aminu, or Turner). Dalembert's replacement doesn't have to be a center, just a defensive anchor (this includes above average rebounding) like Duncan, Garnett, etc.
Possible candidates in draft: Derrick Favors, Ed Davis, Cole Aldrich, Ekpe Udoh, Hassan Whiteside
Possible candidates on team: none
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"The Stretcher"
The Sixers desperately need someone who can stretch the defense with three-point shooting. You might think Jason Kapono can be that guy, but he has major issues. He can't do anything but shoot. He can't create shots for himself. He can't create for his teammates. He doesn't get to the free throw line. He doesn't excel in transition. And he's a below average rebounder and defender. Not to mention the fact that he takes more long two-pointers than anyone not named Willie Green. The ideal "Stretcher" is someone who shoots extremely well from downtown, isn't afraid to take big shots, and brings at least one extra dimension to the team. Whether it's defense, rebounding, athleticism, the ability to create shots, "The Stretcher" needs to do something besides shoot threes. Or at the very least, not completely suck at everything else.
Plus, it'd be fun to have someone on the team named "The Stretcher".
(The Sixers excelled with Donyell "Donny Ice" Marshall for a reason. He not only stretched the D with his range, he took big shots, and brought decent rebounding/basketball IQ to the table. Unfortunately, he was too old to play a significant role, but you get the idea. What Donny brought to the Sixers in '08 is the bare minimum of what the team needs moving forward from "The Stretcher".)
Possible candidates in draft: Wesley Johnson, Xavier Henry, Paul George, James Anderson
Possible candidates on team: Jodie Meeks