Running Pleco 3.1 Beta on an iPad 3, I added some items to the new right-swipe toolbar. The first time I added about 6 items, the toolbar stayed blank. Going back into Settings, the toolbar items I set had also disappeared. This only happened the first time I made a setting; the second time I added fewer items, they stayed.
Some UI points: Personally, I would prefer the right toolbar items to be at the top of the screen rather than at the bottom, or perhaps even better, centered at middle height. What I think would be very nice to look at and work with would be a slightly transparent, circular dial of larger icons that comes out of the right edge and feels somewhat similar to the Mac OS X Dock's behavior. (like the very left part of a circle) The larger icons could be self-explanatory, so they could come without any text description on the right side, making the right sidebar narrower and covering up less of the screen. But maybe if you are planning to extend the right sidebar to be populated like the left sidebar, this wouldn't be feasible. Alternatively, the sidebar could be made only as high as the items it contains.
I think it's a little harder to make the right-swipe sidebar appear than the others. The sidebar on the left and especially the iOS 7 sidebar from the bottom seem to be much more sensitive. Only when I swipe in quite slowly from the right edge does the right sidebar appear regularly.