Honestly this whole push for iDIN integration seems nonsense to me.
First of all we have to keep in mind that bunq is an international bank and provides their services to 28 (and more?) countries.
To expect them to implement about 30 local flavours of identification and authentication protocols is simply absurd, more so if they all turn out to be commercial like the Dutch iDIN. If all of them would charge the same fee iDIN charges just for the rights of implementation then bunq would need to pay almost €2 million. And that's not considering the additional fees.
Secondly, I don't think it is a task for financial institutions to identify and authenticate people regardless of the fact that the Dutch government pushed them to the front lines for this task (due to their own incompetence). Besides I don't want to be dependent on my bank for authentication, if only because it gives them too much power in case I've got a dispute with them. Nor should we move to a US model where private corporation get to hold power like this. iDIN is simply a pet project of the Payment Association to accumulate some extra income.
Thirdly, the government is working hard (or so we hope) at a successor of DigID to make stuff like this possible so that one isn't dependent on organisations like iDIN and Idensys which were aptly called 'authentication pimps' by one researcher. Personally I'm a fan of IRMA https://privacybydesign.foundation/irma-explanation/ but that's beyond the scope of this topic.
And lastly, for all the people here that complain, aim those complaints to the organisations that 'force' you to use it. Most of the examples that are mentioned (e.g. the Dutch lottery, BKR, insurance companies) are fallacies. They all offer an alternative as they should since they are mandated by law to do so. If the alternative isn't to your liking, then don't blame bunq, blame them.
Why should you be forced to handle stuff by old fashioned mail if they clearly don't care about receiving hard copies evidenced by the fact that they'll gladly accept iDIN, meaning that handling it over email should suffice as well. Personally I prefer sending in a copy of my ID anyways, you should (as is your right) censor all but the relevant parts of your ID and put a big red text over it indicating for whom it is meant and for which use with the instruction to destroy the copy after it has outlived it's use. The benefit of this is that your financial institution doesn't know what you're up to.
Not to mention the fact that a little perspective can't hurt either, it's not like you're asked to identify with iDIN on a daily or even weekly basis. Signing up for an insurance, getting your credit report from the BKR or signing up for/receiving from a lottery are typically one and done kind of actions, let's not act like we're severely gimped by the lack of iDIN support.
I wouldn't want bunq to squander €60k up to €2 mil depending on how many countries have a 'unique' authentication service for something like this, that money could be put to use on something really useful. I go to bunq for my financial services, the government (i.e. my ID) for identification services, the grocery store for my groceries and the bookstore for my books.