Maybe so,

But I bet that if Fanjita found an exploit in the PSP's XMB which could allow unsigned code to be run, he would develop that instead of the GTA exploit as it would be more accessible to more people, and he would make an eBOOT loader very similar to his TIFF one (for Firmware v2.00.)

THEN if Fanjita (or anybody else for that matter) had found this kind of exploit someone else would use this exploit to create a downgrader. (IF the new exploit allowed Kernal access.)