A major rework? Probably not.
Slight touch-ups IF they're too weak? Likely.
Generally speaking, Riot seems to be moving assassins away from being able to kill everyone indiscriminately, and make them more focused towards actually hunting down and killing squishies.
AD assassins will probably be in a decent spot once the dust settles. They're losing the current core build, with the early power spike of Brutalizer and the all-purpose power of Last Whisper, but get better AD items in return, like the redone Ghostblade, the access to cheap, offensive CdR in Caulfield's Warhammer without the draught of useful upgrades Brutalizer had afterwards, get a sustain option that covers their abilities and auto-attacks, get a more powerful anti-AP option in Maw, a more offensively tooled Black Cleaver, Executioner's Calling as an option against that pesky Lifesteal of ADCs...
AP assassins will be hurt a bit more, with the general increase in MR. However, AP assassins now get the option to snowball the game right out of the gates with the new Dark Seal - you'll never want to die against that LeBlanc, like, ever.