I'd love to move Thornton for [Seraphin] or anyone of value but there are a couple of problems in this particular scenario.
First Seraphin can't be traded until December. Beal will be back well before. They are projecting 6-8 weeks. Even with caution that puts him back before Thanksgiving.
Second, the Wiz aren't exactly hurting for scoring options on that team. They have Gortat/Nene who are both capable scorers as well as Wall and Pierce who can eat up shots. Young guys like Rice and Porter will probably both get some run at the SG spot in Beal's absence too. Of those guys Rice and Porter could easily check the opposing SG from a physical standpoint.
And, not that this is a problem in the rebuilding phase but, Seraphin always struck me as a PF. He's 6'9" and athletic but I'm not wowed by his post presence. I'd rather have a guy with legit size than eat up a roster spot on a offensively challenged, undersized center. That is why I was genuinely pleased by snagging Zeller, even if his preseason was a pile of garbage.
I'd love to look at Seraphin and think, "Oh yeah he could be the next Serge Ibaka" but I just can't. He's almost 25 and you (usually) know those things by this point in a big man's career.
Nice idea though!