TL;DR: hosted lists aren’t really a thing anymore and anyone doing it is unlikely to do a good job at it.
I used to work for an email service / software provider and recently asked some contacts there about this (hosted lists) sort of thing. It's really not so much that it's not a cool thing anymore so much as marketing and transactional messages are the only ways to make money sending email. My former colleagues said that everyone has gotten out of the list hosting business because they can’t find a billing model that works.
Overhead in list management is pretty high for a few reasons. One is that people who want easy-mode lists often tend to have high support costs. The service also tends to get abused by spammers (who are happy to pay a pittance to force-subscribe people to a list and blast out messages), which is hugely expensive for ESPs. This is expensive because you can't colocate lists in IPv4 space (otherwise spammer and good sender behind the same IP results in good sender failing to deliver messages when the IP gets added to a DNSBL). IPv6 space with poor reputation on just a few addresses tends to have the entire allocation blocked.
Because of this, to run such a service, you need to charge fees that aren't really commensurate with the service provided just to handle the support cost for easy-mode folks, support cost for folks wondering why their list suddenly no longer gets delivered to gmail users, costs associated with acquiring additional address space, and costs associated with spending time to validate your customers are acting in good faith. Barring some sudden advance in deliverability/reputation management, I don’t think that reputable companies who can do a good job delivering messages are going back to list hosting.
I've thought about making an improved list management system for self-hosting, but a combination of having already been scarred by worked in email for half a decade and ENOTIME have impeded that. If anyone else is interested, I could probably be convinced to spend some cycles to help.