I think it is a bad strategy for two reasons:
First, shelving "premium" inventory means that lots of domains will not be available to qualified end users (possibly through a RFP process), that could otherwise develop them into meaningful websites and enhance the standing of the TLD. TLDs don't shine without development.
Second, the market value can go down very quickly past the launch phase and when the excitement and initial interest has waned.
.mobi is the best known example.
In the first two years, a number of premium keywords sold for 6 figures (you remember one guy was actually willing to pay 600K for music.mobi until the auction crashed).
Then poof - nothing.
A few months ago, .mobi domains like realestate, properties, hotels have dropped and were snapped easily.
In the history of domaining, there has been never a TLD losing so much of its value.
The registry has retained an inventory of domains like sex.mobi, that could have fetched good money back in the day. Now they could barely give them away.
In other younger extensions, the value has not appreciated either: .biz .us or .info are worth even less than in the past.