Yeah, the Wallace signing drops the available space, even in this scenario, to $11 million, and cap holds (about $450 K each for 7 additional spots - $3 to $3.5 mil) brings it down to $7.5 - 8 million with a $53 mil cap. Why would Pierce take an $11 million pay cut to add a $7.5 mil player when it requires losing Allen and Rondo, who are worth more than that? Doesn't make any sense.
If Pierce takes a pay cut, it won't be to make cap room, because the Wallace signing makes clear we're not going to have cap room next year. He might do it to get an extension and give the owners a little reprieve on salary next year so they have more money available to resign Rondo and/or Allen and bring in another midlevel bench player (or starting 2).