Yeah, I initially looked into developing something with this scheme in mind, but decided that it wouldn't suit because it was too clunky (with all the refund transactions, and DOS angles) and only supported bitcoin derivatives, whereas I wanted to offer a lot of '2.0' currencies.
TierNolan's (et al) proposal isn't tenable (especially not for trades where the game theory of profit tied to market bid/ask order book is in seconds or microseconds) until at least we can guarantee that block chains don't orphan and become probabilistically final on the order of seconds or less.
Btw, I think these requirements are only required on the altcoin chain in order to interopt with Bitcoin. Thus afaics the reason you can't implement the proposal is because the altcoins don't meet the requirements.
Thus as I say your marketplace isn't threatened for the moment and if ever the requirements are met by some altcoins, you can enable supporting that functionality and basically become a distributor of clients and then try to profit ongoing on that traffic some how (selling advertising or perhaps charging a microtransaction for every web-based client login as opposed to a captcha). Thus the name "metaexchange" is good, but I would also consider a shorter more brandable name such as meta.exchange, metaX.trade, meta.trade, etc.. I see the following choices are available for domain registration:
emetatrade.com ($6 right now at namecheap.com)
emeta.exchangeemeta.tradeGrab it now!
I strongly suggest you change to a slightly more brandable domain and name.
P.S. I had a fundamental error in my recent discussion with you about "inertia" but I left it as for the moment to keep potential competitors off course (and also to conserve my time for programming). Will come back to that soon to correct. Best we will dig into that once I am ready to go 100% open source (soon again).