As a mathematician, this kind of thing interests me greatly.
But in terms of practical use it's very limited.
For instance, though it's *possible* to query an encrypted database... "It must be noted that... the authors have... used simple and non secure homomorphic scheme and still it takes a huge toll on the performance. For e.g. a 16 bit multiplication takes approximately 24 minutes."
This seems inherently impractical and it doesn't look like something we can parallelise in order to speed it up, or anything that any sufficiently large database (to be useful anyway) would be able to utilise in a general fashion for everyday queries.
Sure, you could farm off the database and all such computation to the cloud (that is after all the point - you ask an untrusted third party to do work on a database that they hold but cannot ever determine results or data from), but I can't see it being practical any time soon.
If a 16-bit multiplication takes 24 minutes, imagine how long any kind of complex SELECT statement is going to take, let alone whole-database UPDATE WHERE operations, etc.