Who is going to protect it ? 24/7 ?
Who is going to fill it up ?
WHo is going to pay for all that ?
Most vending machines get attacked and vanadalised regularly ,and they only have
candy and drinks in them
if there is going to be one that contains virtual and fiat money its going to be a target for theives ,this goes double if/when bitcoins are more valuable in the future
The machine above is a close cousin of this
machine, which regularly does
contain fiat money 24/7 and has been built with a commensurate level of security. You might find it at your local carwash which is unattended 24/7.
Besides, it'd be more of a novelty. Something to display at a tradeshow. I don't really own any public-facing property where bolting it into a fixed location would make any sort of sense.
Also, such a thing probably wouldn't actually sell Casascius Coins. Rather, it would make far more sense to sell redemption "tokens" that they must redeem for BTC online, where they would receive the exchange rate at the time of redemption, rather than at the time of purchase. This way, the machine doesn't need connectivity to the Internet, nor would it need any major magic to deal with oddities in the denomination (e.g. not being able to sell less than 1 BTC, a problem when BTC>$20, or requiring exact change)
Essentially they would be buying a "Casascius Mickey Mouse Dollar" which could be used to buy bitcoins at a later time. The secret key could be much shorter (since it's merely a website redemption code not a full private key) and no holograms would be needed (dropping the price greatly, and also dropping the production difficulty, since I could bulk-laser-etch codes on coins in mass quantities and produce thousands per hour, singlehandedly).
All of these caveats would be admittedly less cool than vending real Casascius Coins out of a machine, but it would eliminate most of the costly complication, keep the markup as razor thin as possible, and importantly, would represent a setup where anyone could repeat it simply by ordering a machine, stocking it full of easily-acquired tokens, and then running some open source redemption software on their web server to enable redemptions.
All that said, each coin could still have a QR private key in addition to the redemption code, which would be funded upon redemption (as the way of delivering BTC to the customer), so they still end up with a real physical "bitcoin" in the end.