You can't just assume that everyone will honor the "protoshares" as equal to "bitshares" when they are released though. That's a big part of open source software, people can change it as they see fit at any point in the future. It's at least equally likely that once you release the source code for Bitshares everyone will simply use a version which strips out any sort of previous mining or initial coins. There's actually a big incentive for future miners to ignore pre-mines like this. Imagine if Bitcoin had had a pre-mine of some sort (even in the form of another currency that gets hard coded in to be equal to Bitcoins); likely the first action of the community would have been to hard fork and start from 0 coins.

I have been skeptical of your project from the beginning since you seem to assume that the market is magic and will do whatever you want it to regardless of profit motive. However I was planning on mining Bitshares once you got things figured out. Mining protoshares just seems like a waste of time and effort for everyone involved. I encourage you to scrap this idea and work harder on Bitshares themselves (since any real attachment to a currency only comes from its unique utility). At least you are going about this whole thing more honestly than Dacoinminister with his demands of money up front in exchange for a 100% pre-mined non-functional alt-coin.