I assumed those percentages were just totally made up to demonstrate the idea, not a concrete proposal.
No yeah, I get that. My critique was meant as an example of why implementation matters so much in a product like this. Because without even a rough estimate of how the index would be composed, it's hard to give any kind of feedback really.
EDIT: also, the btc bias comment was meant to generalize beyond just that example portfolio, because as a potential 'customer', I felt it should be made clear that btc is what I hold when I want liquidity, therefore it seems redundant to allocate any significant portion of my investment portfolio into an asset that I'm already going to be maintaining for everyday use and casual savings anyway.
> ... buy the top 10 coins weighted according to some measure, and rebalance once a week
As a relatively sophisticated investor myself, I'm not against the idea, but whether or not I'd invest in it would depend heavily on the implementation. And as of now with that example portfolio, I definitely wouldn't invest in it. Having a large btc bias when all the major cryptos are already highly correlated with btc seems redundant, and rebalancing once a week seems like overkill. Also, marketcap is a poor indicator of returns, in case you're considering using it for weighting.