Would be nice to be able to centrally manage subscriptions through your bank. Or perhaps better yet, to roll them into
taxes, which would avoid some issues going through banks would cause, and offer a nice symmetry to how one-time purchases work.
To me, all those subscriptions have a management overhead that's often greater than their sticker price. Here, $30/month is actually better than $3/month, because there's only so many $30 things that will fit into my "I like it but it's not a strit necessity" monthly budget. But that same budget will fit 10x as many $3/month subscriptions, and the amount is small enough that it's easy to ignore, and it's easy to lose track of all such subscriptions (and then tracking them down and re-evaluating whether you need them feels like more effort per subscription than that $3 or $1 or whatever).
The bigger overhead, however, is relationships. Each subscription is a business relationship, and one I do not want to have. This is where the tax angle, and aforementioned symmetry with one-time purchases, would come into play: for regular one-time payments for goods and services, I do not need to establish ongoing relationships with the providers, because government does it for me. It rolls them all into a neat package by means of generic consumer protection laws, which allow me to not care or remember about any particular vendor if all is right, and if something goes wrong, all I need is to have a standard proof of purchase (receipt or invoice), and a set of standard keywords to put into an e-mail ("warranty", "non-compliant goods", "GDPR", etc.), and things magically right themselves most of the time. Worst case, I need to also remember which form to fill to get courts involved.
That's such a huge win, that most people don't even see it. Whenever you go to buy your daily bread, or get a haircut, you do not need to stick to the same vendor, or sign a contract with them, or otherwise care about ongoing relationship. You can, if you want, but you do not have to, and that's despite the vendor very much wanting you to. The relationship exists, but it's managed for you, centrally, by your local regulator - making purchases O(1) with respect to number of vendors. Whether you shop at one place or a thousand, the overhead is the same.
I would like that to extend to recurring services too. There is absolutely no need for a random SaaS to force me into having a relationship with them. I would prefer to have a standardized process of billing and resolving disputes that lets avoid having to study everyone's individual ToS, or dealing with vendors' dark pattern bullshit. I want to focus on making use of the service, not on who provides it. That's the symmetry rolling subscriptions into tax system would provide.