It's not really an uncommon layout--many older winkeyless keyboards were like that.  This layout is popular because of its left-right symmetry.  Basically it looks nicer.  But yeah, you need sets with 1.5x, 1x modifiers and 7x spacebars.  Or also buy tsangan kits.
I've gotten a couple of DCS spacebars in 7x length from SP for that reason.  But now my new sets will be ordered with tsangan kits right away 

.  I would recommend the ''GKH'' gray for that thick PBT set.  It's close to the color of modifiers.  I have that color spacebar and that pbt set.