Oops! Sorry, I did not see the other thread.
Anyway, there is a lot of speculation in the HP fan community of what this might mean...
The most popular theory is that "hallows" refers to consecrated objects - in the legends surrounding the Holy Grail there are objects referred to as hallows, and these include a sword, a staff, a cup, and a pentacle (locket).
And...oh look..two of those are already what we know to be horcruxes (the locket and the Hufflepuff cup).
So the "deathly hallows" would be the "deathly consecrated objects" - i.e. the horcrux.
And since book 7 is going to have to be about the search for and destruction of the horcruxes, it makes perfect sense.