Well, yes, but a $16,000 price tag would take years to pay back with presumed fuel savings (I don't know what the particular Toyota diesels are capable of). DIesel option on a new vehicle can be much more economical, when it's offered.
This dance is done on almost a daily basis at the Toyotya Motorhome site and it comes down to the following points:
1. The swap is very expensive and will never result in a ROI.
2. The Toyota diesel engines that were actually imported to the U.S. are fairly puny. There were actually a few Toyota diesel motorhomes built in the early 80's. Slower than slow....
3. Most of the swaps have to be done with engines that are imported by the installer, for which few parts are available in the U.S.
4. Resale value of a "Swap" is always a crap-shoot, see #1
A better bet: There is a shop in the San Diego area that installs 5 cylinder Mercedes diesel engines into Toyota chassis for about 1/2 that price.
I actually know people that do this swap with VW TDI engines. There is section for engine swaps over at WWW.TDIClub.COM. With the large aftermarket on those engines there are people pushing 200 to 300hp from a 1.9L diesel. Of course the top end of the spectrum are rare and take a special breed to own.