Interesting post. I don't think we can extrapolate from the current stock market valuations of companies though. Especially not since holding coins is not comparable to owning shares. With crypto you don't own part of a company.

How to get to same estimations is quite challenging and I am certain it differs per crypto. For instance, if you want to take a swing at the future market cap op Bitcoin, you have to make assumptions. If you see Bitcoin purely as a store of value (assumption 1) and believe it will take over 10% of the function of other stores of value like gold (assumption 2), you might speculate about a value per BTC of €XXX.XXX.

For Monero this might be a very different story, and for something like Siacoin you should look at totally different things...

Hope somebody else here has good ideas on how to come up with some possible future values ;-)