I think 4% is still a fine thing to plan around. I don't think it's wise to plan as if today's treasury rates will last your entire retirement.
You can lock in today's treasury rates for 30 years by buying a 30Y treasury bond.
So, yes, they will last if you understand where to put your money. The options are extremely numerous and plentiful now in cash flowing assets, and you don't have to deal with the uncertainty of selling off principal in down markets to finance your retirement
For many, retirement is first and foremost about generating a stable income. A guaranteed lower rate of return is usually desirable over a speculative higher rate of return.
[0] https://www.treasurydirect.gov/marketable-securities/treasur...