I hate it that I can't install alot of app due to it being in Device Memory. I barely use the internal storage as my media files are in my (Ext) Micro SD card. the DM fills up easily, and could not install or update app when it's around 130MB, which should be plenty. I had to manually move some app to Internal Storage, and not all apps can be moved.
FYI, I have an Xperia SP, Xperia Z and Xperia Z1s and Xperia L and Xperia M. All of which have Device Memory and Internal Storage merged. Z1s (26.11GB), Z (13.8 GB), etc. it's awesome, would never fill up, except for the L and M, and possibly SP.
Can the same be done for the Xperia T and TX? custom ROM? Root? CyanogenMod? btw, I never done any of this except flashing ROM. so if it's possible please post links for instructions.