Wonder how long my 8.1 should last

Do we have anyone posting that has 200,000 miles on their Class A ?

Assuming you keep up on the maintenance, you've used maybe 1/3 of the engine life.

That means you will likely be looking at it dying somewhere around 2045 and the rest of the RV will likely have fallen apart before the engine dies.

The owners manual states that the engine was designed for at least 200,000 miles with normal maintenance. Mine is pushing 90,000 and I use one quart of oil every 5000 miles or so.
That does not mean that things bolted to the engine will last that long. I've replaced the alternator, plug wires, fan clutch, fiberglass fan, and a few other minor items.
My Allison transmission also has the same mileage and has needed nothing other than scheduled fluid changes.

With proper maintenance and good driving habits X-2 200,000 plus

Only time can answer that. I've rarely had a vehicle fail because of the engine itself. Usually when I get rid of a driver it is not because of the engine, but other things such as the transmission and overall assessment of age and things falling apart.

With the introduction of computerized fuel systems instead of carbs and chokes with cylinder wash and oil dilution, basic engine life has increased a great deal. It's very common to run a car engine for 200,000 now days. Of course a MH engine is under more stressful conditions than a car but it still has the benefit of the improved fuel delivery system.

Time and poor maintenance are now often issues for modern engines. Lack of coolant changes, loss of a water pump/overheat, deterioration of the radiator core fin bond/heat transfer, ignoring codes and ruptured old hoses, blown belts can lead to the death of a modern engine before it is actually worn out.

I have 84 K on my 2004 Southwind and hope for another 100 K