Well, it could kinda make sense. Bruins are in good position to repeat, maybe even three-peat. Getting Iginla to achieve that, a decent prospect for the future plus what should be a fairly high 1st round pick isn't a step backwards in my opinion.
The only thing is...can they afford it financially. Seguin's contract is pretty cheap, and the Bruins already have a lot of big contracts on their payroll. So financially, I don't think they would do it...but talentwise, I could see them being interested by a package such as this.