Could Class A, well let, CBD, major city offices lose 50% of their value?

 Drivers: 

• Decentralisation, the costs of operating in places like London/ NY are too high  
• Remote working leading to less demand, particularly smaller businesses 
• More supply being built, cranes everywhere in major cities 
• The middle market being hollowed out in many industries meaning fewer firms will pay for prestigious offices and will take less space 
• Ground floor retail units worth less as footfalls decline 
• Higher interest rates pushing up cap rates, from 4% cap rates now
• Pensions selling as they get hit with duration losses on Fed hikes and leveraged RE players squeezed out 

The only positive I can think of is that after they fall in price, if you own them then you own a cash generative, cheap, real asset, which you can finance with paper, negative real rate, yielding debt. But that requires a price fall to set it up first.  

http://wolfstreet.com/2017/06/07/next-asset-bubble-cracks-its-so-big-even-the-fed-is-fretting/