The more general inability to retrospectively apply rules (and access to the ombudsman) to unregulated firms for activities prior to regulation has been known about to everyone for years.
I think a similarly related problem arises where a regulated entity closes down and customers can no longer access the ombudsman because the ombudsman no longer has jurisdiction. I think the UK dealt with this issue years ago (IIRC by making successful complaint claims chargeable against the equivalent investor compensation funds, but don't hold me on that (or anything in here for that matter lol!)). This was I think a problem with potential point-of-sale misinformation / failures on trackers from brokers that largely don't exist any more.
I know the Irish financial regulatory and ombudsman system is relatively allergic to considering Unfair Contract Terms (particularly when compared to the UK FCA, who have a huge amount of guidance and experience considering it). But in this specific case I wonder what the position would be in terms them having activated explicit or implicit contractual terms to effect the original assignment of the loans to the vulture funds / credit services who were not regulated.
The customers would seem to me to have lost a legal right to refer a complaint to the ombudsman and I imagine there'd be a good argument to say doing that was in effect enforcing an unfair contract term by virtue of the loss of a material consumer legal right.
If I'm right then the effect of that could be interesting - either rescinding the transfer (unlikely) and transferring it back (impossible if the entity no longer exists), or holding the transferor liable for the loss of right (and some compensation to account for that, although that may not be any good if the transferor no longer exits or has no assets, note my point on the related problem above for regulated firms that no longer exist).
In any event I'm not sure legally they can ever hold the firms to account for activity when they weren't regulated (hence, I'm guessing, the AG being mentioned in the CBI's feedback to the committee, in order for the AG to deliver the bad news that it can't legally be done). So saying it's an issue that needs to be fixed is possibly disingenuous at worst, hot-potato-passing in the middle, or wishful thinking at best.
The UCT angle may be the only legal course of action but I'm not sure where that ends up if the entity no longer exists / is no longer regulated.
www.independent.ie