AMS to FCO on KLM

More than possible provided the flight is on time. Luggage at FCO is no different than any other airport. It is a busy airport and sometimes we were close to first off and other times the latter half. It is dice roll.

I flew ITA non-stop from LAX to FCO with a checked RS carry-on - the bag, of course, arrived as well, although with a bit of a wait - perhaps because we breezed through the immigration check. Since you won't have to deal with immigration, I would expect a wait for the bag.

Of course, if the flight is late arriving, the connection could be tight.

I also flew to Poland recently on KLM with connections in AMS - the bag was waiting for me at both final destinations.

Why not take the direct easyjet flight to Naples?

Another consideration is your flight may park on the tarmac and you will have to wait for a bus to take you to the terminal. The buses wait til they are packed before they leave the plane.

Possible or crazy?

'Possible', but everything has to work at or very near to perfection to be successful.

(If I had that plan I would probably go through a couple packages of Tums, starting the night before.)

I wouldn't call it 'crazy'; perhaps 'aggressively optimistic' is a better term. (?)

It' arriving at LUNCH time at FCO, and odds are high it will be parked on the tarmac. The buses will be waiting, however, our experience is that the bags won't be. On flights from either Palermo or Oblia, we waited for bags until slightly after 2.

Why not take the direct easyjet flight to Naples?

I booked KLM through Delta with not very many SkyMiles, and my (refundable) train tickets are less than 20 euros each. EasyJet is over $400 by the time we pay for a checked bag and extra legroom (my husband is 6'3").

I just checked trains for tomorrow to compare and looks like it'd only be about 100 euros for the fast train so I guess I'll take my chances on what I've booked and I can change our train on the way to Termini if we have to. I'll let you know how it goes.

Thanks everyone!

The Frecce to Naples are on a shuttle schedule, so if you miss your preferred train, there's another within 30 minutes. If all goes well, you may have time to assemble a picnic lunch for the train at Termini.

An update:
We did not make our reserved (cheap) Roma Termini to Naples train. The flight arrived mostly on time, fetching bags was fine, but it was a nightmare getting to the Leonardo Express. Long walk, stairs were blocked, line for elevator was - no exaggeration - 100 people deep. Elevator only holds 4-5 people with luggage so wait was long. Maybe if we were more familiar with the airport, we would have been able to find a better way, but we aren't and we didn't. And the Leonardo Express was not just standing room only, it was packed so tightly we could not move our feet.
We would typically have taken a taxi, but since it was just two of us traveling, I was persuaded by many "it's so easy and cheap to take the Leonardo" comments. Never again.