After watching a bit of GTA 5, I had an idea based on it's Option C ending.

After the events of The White House Heist, Ending 1 (Bain dies ending,) and before the PAYDAY crew retire, your crew is laying low to drop the heat. Locke calls in to inform the gang that he finds out through tapping into the FBI's communications that the FBI, the SWAT team, and Murkywater are all working in tandem as a one-strike squad aimed to take out the PAYDAY Gang -- permanently. With the Murkies on their last leg, and the FBI and SWAT losing countless battles with the heisters, this would have to be their final hurrah -- their final stand to tackle the crew and bring them to justice... Or to the cemetery.

The heist would play out similar to holdout. The crew would be restricted to a medium sized play area with decent cover and lots of areas for the enemies to spawn from. A large warehouse, full of machines, terrain, and crates to hide around and tactfully deal with their threats. Unlike in Holdout, however, it would just be a survival situation. Your crew vs the world. You would have the FBI cops, the SWAT (or ZEAL team if playing on Death Sentence,) and Murkywater units all spawning and attacking the players. The crew would need to survive for a set number of waves until the enemies give in and the escape arrives.

I don't know if this will actually be doable or not, but I think it would be a good challenge for custom heist makers.