This is a fairly simple spell which I have previously implemented in NWN1 games, which provided concealment enough to hide, forced people to actively maintain targeting to keep hitting stuff within the AoE, and prevented sneak attacks, per this clause in the PHB:
A rogue can sneak attack only living creatures with discernible anatomies—undead, constructs, oozes, plants, and incorporeal creatures lack vital areas to attack. Any creature that is immune to critical hits is not vulnerable to sneak attacks. The rogue must be able to see the target well enough to pick out a vital spot and must be able to reach such a spot. A rogue cannot sneak attack while striking a creature with concealment or striking the limbs of a creature whose vitals are beyond reach.
Which leads me to believe that we should really be looking at ways to make up for the roguey shortcomings before implementing protection against their primary means of attack, and I'd really rather not see spells put in with partial functionality. Most of the use of huge concealment-generating spells like obscuring mist is in the protection against sneak attacks and the ability to hide in them.