As I mentioned above. If there is competition between miners then as the block reward goes to zero so do the total fees per block since the "penalty" in terms of block reward is less than that in Monero. At this point there is no incentive for the POW and the coin becomes insecure. The alternative is a mining cartel or monopoly that sets minimum fees. Quite apart from the centralization involved I have serious doubts  such a cartel will be sustainable in the long term since individual members will cheat.

A good current example is Bytecoin which is for the time being is secured by the Bitmain ASICs. The question in my mind is how long will this last as the block reward continues to fall.  The current block reward in Bytecoin per block is ~1200 BCN if one applies the 10^4 factor that would be equivalent to ~0.12 XMR or about 20% of the tail emission in Monero. By the way I prefer to see Bytecoin as the canary in the coal mine for falling block rewards as opposed to the scam in the pre or ninja mine.