Yeah, and I want to turn water into wine as well.
That's a very good example of a post that is both unhelpful and not related to the conversation, the exact reason posts like this become long and hard to traverse.
You may try to convince MikroTik to implement some broadcast relay (I've seen programs for Linux in the past). I'm sure you wouldn't be the only one who would use it, but I also don't think that demand for such feature is any high, so I wouldn't count too much on them saying "yes".
So I'm not looking to add a new feature, but just see if there is anything that exists. I've heard of DST NATing to a unicast address, but again not helpful. It's definitely a frustrating situation, as the software development company is extremely unhelpful in trying to come up with a solution.
Except the fact that it would break the standard restricting a broadcast domain to its own subnet, this could be a useful feature.
It would enable e.g. workgroup/SMB browsing across subnets without using a WINS server. But this tends to become kind of obsolete.
With PIM and IGMP Proxy, it seems you can restrict the source of the rebroadcasted packets, which is what I was hoping for here. That would help to keep the broadcast domain restricted.
Thanks for the replies everyone. Maybe someone will have an idea.