My approach is trying to keep flexibility so that Memehub can adapt. If getting memehub users to hold their steem turns out to be a concern, then we could implement a minimum Steem Power amount to be held by the user before they can exchange their LULz, or something to that extent for example.
Since Memehub is accessible to non-crypto users, the ad based model becomes feasible for sustainability. I have other ideas for monetization such that it is not at the expense of the users, steem, or memehub itself.