I think those are all good points, but I think they’re also potentially surmountable ones; I think the key would be to be as restrictive as necessary for which mods are allowed to charge. If only a small fraction of the most clear cut and expansive mods can charge, maybe even hand-picked by the developer, I think that’s still a better state than it was before.
Some potential examples: a mod isn’t allowed to charge if it has any mod dependency. Games supporting paid mods must support opt-out updates (steam already supports this easily via "beta branches) and mods have at least one version available to consumers that are guaranteed to work. Depending on the mod, it could be possible to do some automated regression testing, similar to how the Steam Deck verification works.