I'm a big Blackcoin fan but the concerns you raise are valid. Some proof of burn coins use multiple coins for the distribution and limiting it to one coin does warrant scepticism.  

The advantage of burning from multiple coins is competition. The weakness though is that the added complexity of multiple coins gives more means for manipulation. A big whale could pick a coin with the lowest volume and drive down his own entry point to get access to the burn coin. That's much harder to achieve with a single point of entry.  

Bitcoin itself is not actually that well spread. The amount of active users may be much higher but there are huge whales amongst them.  

The main reason why Blackcoin is the suggested source, as laid out in his blog, is because the protocol of Ercoin is nearly identical to Blackcoin. It's the same PoS, it's the same launch principles, the same protocol. It's practically Blackcoin written in Erlang. And this makes sense because Blackcoin is a very pristine coin in this ecosystem. There's no premine, no ICO, no developer fees on transactions or on the staking, the distribution has been completely fair and transparent.  

The reasons for using Blackcoin seem pretty obvious, but if I were an outsider I would too wonder why specifically this coin. I think it also leads to the question what exactly makes Erlang so much more valuable that it warrants a new coin. This may be personal ignorance but the added value at this moment seems quite abstract.  


Technically there is a cap, that of Blackcoin. Though practically saying any real practical cap that would be (much) lower than Blackcoin would be bad as it would create lots of opportunities to leverage the launch. Making the potential cap go as high as it's burn source is legit, especially on a coin that's well distributed.