So for ex: Monero devs make another coin purely for transactions called Mon. Once Mon has bloated enough, then they replace Mon with another coin called Mon2, etc etc, or Mon automatically does this for itself.
If you instead mean another block chain, realize it too has to be public viewable else it can't be secured with PoW.
If darkotas Mon, or another block chain was public viewable, what then?
Neither can scale fast enough so XMR to reach 10 million users in 3 years, because XMR would need to scale 10^3 in 3 years.
And there is a computation issue on verifying transactions if you want to scale up micro-transactions volume (e.g. 100,000 txs per sec):
But doesn't Bitcoin only have around 1million users atm after 5 years? Though I should probably account for the fact that prestigious altcoins would gain a larger following than Bitcoin in it's early days since the cryptocurrency sector has a lot more people now.