Aesthetics of solids vs flowing liquids aside, resin just doesn’t hold up very well under constant UV light. I don’t want to know what it would cost just to tear it up, nevermind replace it when that happens. Unless there’s some super resin I dont know about.

Other considerations:

• a million particles would get trapped in the resin before it cures.
• resin heats as it cures which could do massive damage to the basin at such large volumes.
• that amount of resin would be a nightmare to mix/pour evenly and cure quality would be highly dependent on weather. You’d probably have to do it in layers, which just creates more opportunity for debris to get trapped inside.
• wear and tear. I bet you would have all sorts of people and wildlife walking around on it and scratching it up.
• stains from said people and wildlife.
• yellowing and clouding over time, which will make it not so reflective plus plastics in general are a bitch and a half to buff/polish

…honestly you’d be far better off filling it with polished concrete or stone. Just commit to the bit at that point. You can even dye it.