It's difficult to justify anything but AGM...that's why most of the high-end coaches use them.
I just replaced my entire set of EIGHT 8D AGMs for the lovely price of nearly $900 each.
They lasted almost 8 years and have the Pulse monitor system which really helps their life.
As stated, Lithium is NOT a direct replacement option. Not only is even the cheapest battery 3 times as much, but the charging/monitoring systems need to be changed as well. The achilles heal of Lithiums is COLD...as in they drop on their face in the cold. That's why they need heating mats.
So many advantages of better power, deeper drain, and LOOONG life...but right now, the changeover for larger coaches will be a horrific cost.