sorry if this is a bit 'high level' and abstract but basically i think what the mechanism is trying to do is absorb USD (and other fiat) like a sponge into the xrp ecosystem in a way that bolsters price action continually, predictably and consistently, rather than by blindly hoping market makers acting solo (or hoping traders and hodlers) will "overall" push up prices on a promise of eventual gains/utility/etc, which is ultimately circular logic
what i mean by this is, if market makers are constantly buying-selling, then (aside from network fees) the liquidity through spreads gets eaten up, and that liquidity is probably retail/speculation/trading which shouldnt be discouraged because the xrp ecosystem needs it (even little fish like us!) ultimately to provide liquidity that market makers can actually absorb... so...
where does this fresh capital come from? it can't be just market makers changing one currency to another alone since there's a simulataneous buy AND sell; so it needs to come from NEW capital coming in for NON-speculative reasons and NOT exiting on the other side, but staying in xrp -- these one-way payments are the ones where businesses are most keen to just pay to "make it happen" because speed is everything as there are business costs behind it one doesnt see, i.e. the delay to an urgent payment can be far worse than just eating a bigger fee (aka TIME IS MONEY!)
the only mechanism I could think of right away was ONE-WAY payments, e.g. Business A needs to pay Business B in a foreign exchange; we are not "rebalancing" funds in this situation, so a market maker gets a cut of the fresh funds coming in from the "fiat world", and that fiat "stays inside" the xrp ecosystem as either capital/profit for market makers to use (e.g. to buy more xrp!) OR as xrp kept by market makers that was already bought on-market in fiat -- only the market makers are rebalancing their fiat/xrp positions
as fiat gets utilized within the ecosystem by market makers, we get a virtuous cycle of liquidity/spread/price, since MMs only take their scoop from the spreads as a "fee"
so one-way payments, which are also nicely aligned to "on-demand, real-time, just-in-time" are the mechanism by which FRESH capital is brought in and a portion of which is KEPT within the network as a net UPWARDS pressure on price, which can be thus calculated ahead of time; since we can theoretically calculate and predict the incoming fiat kept within the ecosystem, we can also calculate how much maximum "downwards pressure" we can exert at the same time with xrp sales
also, xrp bought OTC (off market) is subject to rules regarding its selling, and, if these OTC buyers are in fact market makers, this aligns perfectly with their utilization of the xrp ecosystem by needing to hold BOTH xrp AND fiat, thus they are never net overselling xrp vs fiat to rebalance their holdings; meanwhile, the FIAT capital ripple (or XRPII Inc or whomever gets to be "in charge" of the xrp pool(s)) can of course be re-injected into the ecosystem (but this time as fiat, causing potential upwards pressure once again -- however, i dont think this happens directly e.g. as xrp buybacks since that would trigger valid market manipulation concerns from ripple-related entities)
the key in my theorizing was that market makers indeed must and will hold xrp for operations and not sell below a given pre-agreed price threshold when they bought OTC, so that XRP only be used for the equivalent USD buy-side
[hope this top-of-my-head rant makes sense...]