Aha! I assumed the query it would join with would need params but I was wrong. (Maybe the phpdoc should explicitly say that either type is allowed, but I guess it doesn't say that in every dml function...)
I get that the changes are probably minor - we have 40 custom plugins with non-null providers, which I realise is smaller than the number in core, but it might still take us a while...
The point about showing warnings if there's data not being deleted (and maybe indicating the lack of support in the plugin registry page?) sounds useful.