BitVM is quietly evolving:

The new design, BitVM3, drastically reduces onchain costs in the case of a challenge (by ~1000x).

In earlier versions, while challenging was permissionless, the high costs meant only a few well-capitalized entities could realistically participate in the process.

BitVM3 may change that, opening the door to a broader set of challengers.

The tradeoff: garbled circuits introduce a multi-terabyte offchain setup.

Reducing this overhead is an active research area and likely to see improvements.