Great question! The "all-or-nothing" fundraising feature is on our roadmap and might happen towards the end of this year. We have explored different options to implement it. It's doable natively on Lightning but has pretty big limitations.

Our current bet is that it would be best to make use of Liquid as an accumulator of funds for the duration of the fundraise. With Liquid covenants we can set a threshold on the amount raised before funds can be sent out of the contract.