Why wouldn't you consider a Kindle? (Note: their builtin dictionaries are considered the best.)
And why are you posting in a thread about moving on from the Sony, if your advice is to stick with the Sony?
NOte that there is a
Kobo developers forum. I am not sure about Android, but I do know you can boot
debian on the Kobo Aura HD.
...
Ah, and
Android at least on the Glo.