Recently I tried to implement IPv6 in our network however I met a problem - DHCPv6 server is not able to delegate ipv6 address. It is problem because receiving ipv6 addresses via stateless route advertising is disabled and thus it is not possible to ping client's routers, which is bad because you do not know if ipv6 is working or not.
So it would be good to have implemented address delegation (including static pool) to be able to set-up ipv6 in larger networks. Without this feature, the usability of ipv6 is quite limited.
Static ipv6 are not a solution. When you want to move the client to another node, you have to do an extra configuration of client's router instead of just changing the SSID of wifi AP so it is easy to forget on it.
It would be good to have this feature in 6.xx versions too.

I have also one note to adding default route via DHCPv6. The client in 6.46 adds ::/0 by default and it is question if it is good as default route should be 2000::/3 afaik.

Even though 2000::/3 is correct, because that's what's currently allocated, IMHO it's better when it's not hardcoded anywhere. Because one day they will allocate more and we don't want to repeat the 240.0.0.0/4 fiasco (the "reserved for future use" block that we can't use, because it's in so many places marked as unusable).

And funny thing, DHCPv6 is not supposed to add routes at all. Those should come from RA. MikroTik's DHCPv6 client simply uses DHCPv6 server's address as gateway, which is not exactly correct, because DHCPv6 server can be different machine than gateway.