Another idea (yeah I know i'm annoying :p) but it might be a tricky one : Have the ability for every coin to specify at what price we bought X amount.
Example : I have a total of 19 ETH on my account balance. I can add the following : I bought :
- 5 ETH at $300
- 10 ETH at $350
- 4 ETH at $700
And with this data generate a column (in dashboard) "General profit" or something to see how profit/loss I make on every coin since I bought it

See ya