" Finally, a question: has the Splinterlands team contemplated the impact that a third party developer may have if they were to build an alternative marketplace that did not use sm_rent tx; but instead did "delegations for x" instead?

Would this not defeat the purpose of this proposed "tx fee" on the markets, and just shift the load (and presumed AWS server costs) - elsewhere?"

For my understanding this would not really work great as in this case IMO the card owner can take back the cards every time and not only to the end of the rental contract (minimum 2 days, than every day).
So as renter you can't be sure to have the card for 2 days, the card owner can take them back 5 minutes after you rent them, isn't it ?