The Brits and Canucks tried something like this years ago with United Kingdom Britcoin (UKB) and
Canadian Digital Notes (CDN) respectively.
One big problem turned out to be that the transaction fees were not sufficient to motivate enough miners to secure the blockchains with enough hashing power to make them even marginally secure against 51% attack.
That problem was temporarily band-aided or splinted by moving away from blockchain format temporarily until such time as the transaction volumes make transaction fees look attractive to Massively Merged miners and Massively Merged Mining matures to a point where being merged mined might reasonably be hoped to secure the chains. The over a year now wait for ASICs has extended the duration of that "temporary" move because of course the people most interested/motivated to secure the chains did not want to invest in mining rigs that were, for a year or so or more, about to be obsoleted in "two weeks" by Butterfly Labs ASICS.
Hopefully once top of the line 28nm or better ASICs are widely available off the shelf on a same day shipping basis the interested parties will be able to deploy mining gear and move back to blockchain format as merged mined coins.
Another big problem turned out to be the cap on the number of coins, since they followed the tradition of bitcoin, (100%-pre)mining only 21,000,000 coins.
Trying to keep the price of UKB at GBP parity and the price of CDN at CAD parity resulted in the Brits and Canucks selling off their coins cheap (that is to say, at parity with the fiat) in their attempts to prevent their coins from going way the heck up higher in price than mere parity. The Martians seem to have been the main beneficiaries of that Brit and Canuck largess, because the Martians did not throw away their coins (
Martian BotCoins) cheap in attempts to keep their coin at some arbitrary low value trying to keep it at parity with some variety of fiat. The Martians happily allowed their coin to go up and up in value, buying up UKB and CDN cheap (as in, at or close to parity with the corresponding fiat), until eventually the Brits and Canucks abandoned their attempts at suppressing the value of their coins.
http://galaxies.mygamesonline.org/digitalisassets.html-MarkM-