NJT is incapable of serving diagonal commutes right now - the frequencies suck, the punctuality sucks, the idea of timed transfers is foreign to it, etc. Forget about it. It can't even do a transfer at Secaucus toward Manhattan right. Even with vastly better industry practices, MOM isn't going to serve any of those diagonal commutes, because at current driving and parking prices in Princeton, only eco-martyrs like me are going to try using the transit system. And eco-martyrs like me don't live in Ocean County. Maybe if Princeton Junction and New Brunswick looked like
this then it would work.
The trains-per-day limit just shows you how screwed up American railroad practices are - they're lifted entirely from freight. Everywhere else in the world, including US transit systems that are not mainline rail, people think in tph. If for some reason you can only run 20 tph at rush hour, you could easily do 240 trains per day in each direction. Capacity limits are measured in terms of headways and schedule maintenance, and those work entirely in tph terms. Tpd matter only if your trains need to be stabled somewhere midday (i.e. your off-peak frequencies suck so much they won't just turn around and keep earning revenue) or if you can't punctually maintain your peak feasible capacity.
Nowhere on NJT, or Metro-North, or the LIRR, is 30 tph done on a double-track line (one-way running doesn't count). Metro-North runs 50 tph into Grand Central, but insists on running trains 3-and-1 on the trunk instead of 2-and-2. I'm told that Amtrak is forced to single-track at rush hour because the LIRR thinks that its ~38 tph into Penn Station can't fit into a 2-and-2 situation. Peak traffic through the Hudson is 24 tph, and New Jersey thinks it can't add any trains.