It’ll be easy enough for them to block fediverser/0.1.0 user-agents, so perhaps that’s not a safe default value since it’s an easy target.

I’ll be honest, I saw a previous post of yours and was sceptical, but I think based on the idea, you’ve taken the best steps to make this a reality. Having the communities be part of instances where they fit in and can be maintained by moderators who care about the subjects is a challenge, but it does set it up for longer success.

As others have pointed out, there’s still an imbalance where people don’t realize they’re replying to shadow accounts (like this for example). Maybe a good solution would be to DM someone who replies to a comment by one of the bot accounts explaining what’s going on. Maybe asking the person who commented to reach out to the user on Reddit directly, and asking them to join the Fediverse would be a good solution and would bring in the human element to the process. This would avoid you having to build that feature (and likely appear to be a spammer) which might have a higher conversion ratio.

I’m not sure if you have a plan for it, but somehow allowing the Reddit user to take over the shadow account would probably achieve your goal of getting more people to convert, and would be a benefit to niche instances looking to grow their organic members. However you do this, it should be seamless to the new member, with the minimal number of hurdles.

Good luck!