The New dev blog even takes all the fun out of reblogging, since they drop a summary at the top....
"Tl;dr AfterTyrannis, for any point more than 10AU outside the furthest celestial in the system, you will not be able to open cynos, create bookmarks, or warp to that location. Also, all "stuff" outside this range will be deleted during Tyrannis deployment."
So, save your effort, don't go rushing to get those soon to be rare deep safes, because they will be swept away soon, and not just the bookmarks, anything you've left parked there is being nuked. Including ship and capsules, if you log off there in May 17th expect to find yourself podded back to your clone station.
At best you might be able to pick up some safespots in some systems that are hard to find because they're way out of the ecliptic, but still within the limit set by CCP, spots that you would otherwise be unable to get to when the logoff in warp bugs are fixed. However these are unlikely to have the kind of utility that true deep safes had, unless the system is truly huge.
Myself, I did some testing on singularity and discovered that logging off in warp freezes your logoff timer until you arrive on grid at the destination of your warp. So there's no escaping arriving at your destination regardless of how far away it is. There is however an odd bug that ships on grid at the other end cannot select 'look at' while they're killing your Freighter.