Another day, another once unthinkable crypto exchange traded fund filing. Canary Capital's proposed Solana ETF has become the second such vehicle to reach the starting gate.In a regulatory filing Tuesday the Securities and Exchange Commission (SEC) opened up public comment on the "Canary Solana Trust," a proposed ETF that would bring SOL investing into mainstream finance.See all newslettersThe filing amounts to a clock-setting for Canary Capital's proposed investment vehicle. In 21 days the SEC will render a verdict (approval or denial) or, perhaps more likely, kick the decision can with deadline extensions.Market observers are broadly bullish that SOL and other altcoins will win their own ETFs this year, but the exact timing and order is unclear. What's more seemingly apparent is the SEC's newfound willingness to look favorably upon the industry, and past the regulator's old misgivings under former Chair Gary Gensler.Donald Trump's return to the White House created an opening for Canary to act aggressively, CEO Steve McClurg previously told CoinDesk. The firm's looking to list altcoin ETFs for assets like Solana that would have been nonstarters under the old regime.Grayscale's prospective Solana ETF reached this starting gate last week, meaning its 21-day fate will come a few days before Canary's – and likely be a "canary in the coal mine" for both.A representative for Canary did not immediately respond to a request for comment.