I think the PL are probably caught in a catch 22 with this because PSR is inherently retrospective, it is calculated over the past three years.
So, if they don't take into account interest on shareholder loans for the past three years, that give those clubs with interest free loans an unfair and unlawful advantage.
But, if they do take that into account and those clubs end up failing PSR it seems likely they'll end up with a similar situation to the Leicester case where the rules are unenforceable because they didn't know or have the opportunity to resolve that at the time.
Possibly the only way it can be resolved is to wipe the PSR slate clean for everyone and start again.