This has been an endless topic of discussion on VW diesel internet forums.
I think you will find that every modern engine design is an interference design. There are too many compromises in the shape of the combustion chamber and the profile of the camshaft to do it otherwise. Getting good efficiency out of the engine demands a relatively high compression ratio with good "squish" (the piston has to come close to the head around the perimeter) and a combustion chamber that is centralized around the spark plug (as opposed to having significant volume in oversized valve pockets far from the spark plug). If you want an efficient 4-stroke engine, it's gonna be an interference design. So you can cast off the approach of using a non-interference design. Chrysler 2.2 K-car engines aren't competitive in the modern world. (Who would buy a car with 82 horsepower nowadays?)
So then it comes down to chain versus belt, and therein comes the dilemma ...
At least with the VW engines, it's true that the chain doesn't have a scheduled replacement interval. BUT. That doesn't mean it doesn't gradually wear out - either the chain itself, or more commonly the guides and the tensioner, and in some cases the water pump if it's driven by the same chain. The problem is that the chain and guides are MUCH, MUCH more expensive to replace. You can take the front covers off the engine and do a timing belt job easily (although I will grant that so-called "mechanics" have been known to screw this job up and cause expensive trouble later down the road). But the chain pretty much requires the engine to come apart, because it's routed through the crankcase (on the lubricated side, as opposed to the belt, which is essentially bolted to the outside of the engine). More commonly, the chain or guides wear out after (say) 300,000 km and then the job of repairing the chain costs more than the car is worth, and the car goes to the scrap heap. Many, many early VW VR6 cars went to the junkyard because of timing guide and tensioner trouble. On that engine, you had to remove the transmission just to gain access to the chain, because it's on the rear of the engine, at the flywheel end. The current (but soon to be retired) 2.5 litre 5 cylinder engine that is the base gasoline engine on VW's nowadays uses the same PITA chain arrangement.
The belt design does require periodic maintenance, and if the owner doesn't pay attention to the maintenance schedule (or doesn't know what a timing belt is ...) then yes, they're going to get a blown engine eventually. German cars are designed hand in hand with that maintenance schedule and thou shalt not deviate. On that basis, every 144,000 km as called for in the service manual, my car has gotten a new timing belt, tensioner, water pump, and idler rollers, and it has now been done twice and is coming up on the third. The independent shop that I go to, charges around $700 for this job.
I don't have a problem with the use of a timing belt in this application. I'm capable of reading and following a maintenance schedule. The only thing I wish they'd do, is design the front of the engine so that you didn't have to screw around with the engine mounts to change the belt. *That* is what makes it a pain to do. On my old '96 Passat, I could do the t-belt myself in about 2.5 hours in the driveway because that one had the old style engine mounts on the left and right of the engine (i.e. front and back of the engine when installed transversely) - nothing went through the path of the belt. On the newer ones, there is a front engine mount (right side of car when installed transversely) that bolts to the front of the block through the path of the belt, so there is no way to change the belt without taking that engine mount off. Pain in the tail!!! On top of that, there is not much room to work, which is why I pay someone else to do it on this car.
FWIW there is a lot of new technology coming down the pipe. The upcoming VW TDI engine in the next VW Golf (due next year) uses a so-called "lifetime" timing belt, but it's still installed on the front of the engine as usual. (Experience with VW water pumps is that you'd best be changing the water pump so that you don't go beyond 200,000 km on it, and that means you'll be changing the belt anyways.) But even more interesting than that ... is the new Ford 1.0 Ecoboost engine (3 cylinder) that is already in production for the European Ford Focus and is believed to be coming here next year to replace the old 1.6 in the Fiesta. That one uses a "lifetime" timing belt that runs in the engine oil inside the crankcases ... essentially non-replaceable without a complete engine teardown (same situation as a chain, but you CAN NOT split a belt and re-install it the way you can use the master link of a chain).
I have a Honda snowblower that uses a timing belt that runs in the engine oil, so it's not exactly new ... but I'm still not entirely convinced that this is a good idea.
