Just had a very quick read through, and the rulings seem to be centred around making SIM cards available to use in other devices, "so basically, you should be free to use any SIM in any device that you want to". I've not seen anything that says data-only SIM cards are banned, or indeed, anything that says that a provider must include a phone service with it's data SIMs. I assume these are designed to be used with Dual-SIM devices, so IDNet would provide the data, and you would stick to your usual mobile operator for phone services?
Likewise, I could be misreading things, but I wouldn't have thought IDNet would have overlooked any Ofcom rulings.