You have a good point here. Would a grace period on name owner switch help?

I don't think that would make much of a difference. SEO is usually a long term strategy.

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Alternatively, we could use immutable ID's as resource links for google, and only have the premium names as redirects.

I am no expert in SEO but I assume that would be a better solution. Of course the premium URL will per se have a better SEO because of the name but it would only be a marginal factor I guess when a link is using proper alt-atribution.