What is to stop the accumulation of encoins becoming so great that it vastly outweighs the size of the encoin economy?
(much as is now the case with bitcoin)
Nothing, really, but there is no promise of future, staggering returns as with the design of BitCoin. But realistically, the only way the accumulation of coins could vastly outweigh the economy is if the economy collapses. An EnCoin won't cost more than 10kWh to produce, so if hoarding becomes the norm, "late adopters" can mine without the fear of the rug being pulled out. They may not see the hundreds of % returns that the sell price promises (assuming a sell off between), but they will not lose money unless coins become so common that they sell for less than the cost to produce. Again, this points to the collapse of the economy, which is not likely if hoarding is driving up prices.
Also, transaction fees must be taken into account. No one can mine 25,000 encoins unless they have done it for decades. The only accounts that will have balances in this range will be legitimate businesses who will have no interest in devaluing their coins for a quick profit (if they would even be capable of doing so). So if a large number of people hoard their small amount of coins, transaction fees will cut large in to the potential profit (and potential damage to the market). Because the more people that make smaller transactions, the more currency is destroyed.
Corporations with good electricity discounts, and consumers in countries with lower rates might build up significant stores with the expectation that they'll effectively get a slight premium in the end due to their production cost being lower than the average.
This is exactly the same scenario as with BitCoin. Nothing can really be done about it. If it is prohibitive to produce coins for you, then you will have to buy them for fiat, or mine at a slight loss. Again though, building up significant stores is a lot easier said than done. Insanely more difficult than with what originally happened in bitcoin.
Don't we then have the situation where a few large holders who need to sell for some reason, could effectively spook the market and also cause a crash in value to well below the cost of production?
Temporarily. Part of the ingenuity of EnCoin is that computational power is not required to secure the network. In fact, I have already added another point to the technical details section that should allow for well-trusted network trusts to go into a "cool down" mode where they would only be required to work for a very small amount of encoins to maintain their trust, but would still be part of the total network trust. So if the value is low, stop (or significantly retard) mining, keep the network secure, and allow transaction fees to increase the value of encoins until it is profitable to mine them again.
Businesses wouldn't even need to base their value of encoins on the current market price. With smart utilization of the network, they could be close to sure that the price will return to equilibrium again (this will, of course, require some history). Trades outside of the markets could potentially go unaffected.
I don't see that situation as necessarily a death knell for either encoin or bitcoin - but I'm just not yet seeing how encoin is guaranteed some price equilibrium approximately near the cost of production. Does the design of encoin allow a determination of how many coins are 'out there'?
There is no guarantee, only the systems I've described that make the attempt. But if the economy is functioning and healthy, I think it will be a hell of a lot more stable than bitcoin. The total number of coins will be an easily available number. Simply add up the balances of all the wallets in the most recent primary block.
Even if a rough 10KWhr price correlation were achieved - the price differential in electricity around the world is huge. For a vast number of people, the value of encoins would primarily be a function of what some other small group of nations paid per KWhr. Perhaps for example encoins will predominantly be produced in the Ukraine with it's cheap Nuclear power.
Again, there is nothing that can be done about this and it is an issue that affects bitcoin as well. It is
less of an issue with bitcoin because the ROI is ridiculously high, but I highly doubt that this will always be the case. If EnCoin becomes a true medium of trade rather than a "check what it's worth on the exchange" type commodity, I think this will have less of an impact than you might think. If EnCoins are cheap to produce in Ukraine, products and services in Ukraine would cost comparatively more EnCoins.