"is something like an ETF or bitcoin futures too antithetical to Bitcoin’s ethos?

It’s completely antithetical. Because what you’re talking about is centralized custodian holders who give you a fraction of the rights that having your own keys gives you. You have exposure to the monetary fluctuation. You don’t have any of the autonomy, empowerment, voting ability, participation ability, authority, and independent validation of transactions that you have as someone who holds the keys and uses bitcoin or any other cryptocurrency directly."