Yeah, I'm aware that ARC was cancelled. The fact that a trans-Hudson subway extension is not really viable anytime in the next few decades doesn't mean that the extension to Chelsea is an alternative worth building, though; it just means that the reality is going to be that Hudson Yards will be a terminus for quite some time.
They have to dig two new tunnels in the next 20 years. Just sweeten the deal and make it three. The new guy could make it happen sooner. The bigger deal is that MTA will have to implement zoned fares to keep from undercutting NJT. That is the unspoken feature that OMNY will be bringing to the city.
The other big deal is that the MTA is not fully funded by fares, and getting bi-state coordination on dedicated taxes is a fool's errand (see: WMATA in DC)
If New Jersey needs a subway tunnel across the Hudson, PATH would probably be a better place to start.
