My own view is that the United States can accept a lower threshold for at sea nuclear deterrence, but this leg should still retain a rump deterrence capability. Survivability concerns may not be what they were, but they are still relevant, and SSBNs have both survivability and flexibility advantages over ICBMs. It isn’t accidental that China, India, and Russia are all choosing to develop or upgrade their SSBN capabilities at the same time. Concerns about shipbuilding costs should be remedied by resource transfers between services; if the Air Force no longer operates an ICBM force, then funding can (at least theoretically) shift towards the Navy. Replacement of the Ohio boats will still be expensive, but circumstances may allow life extension beyond current expectations. The long term answer may not be an entirely new SSBN design, but rather a modified Virginia class boat that could carry ballistic missiles. The Navy has argued that this design would become more expensive than an Ohio replacement, but issues of number and vulnerability may prove more manageable if the option is no boomers at all. No other state in the world can match such a capability, and yet the U.S. presumably feels deterred from launching pre-emptive nuclear attacks on China or Russia. A reduced SSBN force is still the best option for providing a foundational level of nuclear security.To expand a touch, I don't think that the force-stretching problem that typically occurs when the fleet is downsized applies to the SSBN force. You don't need to ask 8 SSBNs to do the work that 12 used to accomplish, because you can achieve deterrence against any plausible adversary or coalition of adversaries with 8 boats. Moreover, it's unlikely that any foe that can't be deterred by 8 subs can be deterred by 12.
I'm also willing to grant that the chances that significant resources might shift from other services to make up for the cost of the SSBN replacement is slim, but it's still worth making the argument; if the Air Force gets out of the ballistic missile business, the USAF's share of the pie should drop. Here's some more on the aging ICBM force.