You still don't get it. The car population is controlled by LTA through the quota allotted for COES yearly, which is pegged against cars DEREGISTERED for that year. Hence, the car population is already controlled in principle. Why do we need to re-invent this control mechanism with a car park method that costs each car owner $100k, as you suggested?
Hence, your suggestion to me is naive, to say the least. It does nothing to control the car population, but instead it brings more problems to the equation, like what I've suggested.
To think out of the box is NOT difficult, but it must be a viable suggestion and your suggestion of car park method is simplistic and frankly, not workable as it does not solve the problem of high cost of owning a car, since, as you said, each car park can cost $100k, besides other problems related to owning a car park, etc, etc.
The COE method is deliberately left to float to squeeze as much revenue from those who think they can afford a car. In essence, it is not meant to control car population, as merely limiting the number of COES issued would have done the trick and then do a balloting. The lucky ones get the COE, at, for example.....$5K or any affordable price to be determined.
No need to go round the mulberry bush to solve the PRICE ISSUE of the COE by suggesting alternative method like what you've suggested (car park method). No need at all as this COE high price issue can be so easily solved by LTA...if it wants to. A BIG IF.