The DHCP server in Mikrotik routers can be configured to supply arbitrary options to clients, and the DHCP client in Mikrotik routers can be configured to add arbitrary options too, but the DHCP client has no method of requesting arbitrary options from the server and does not make values from arbitrary options available to the user script. Several IPv6 transition mechanisms rely on DHCP(v4/v6) options to give extended IP configuration information to the clients. This includes two of the most widely used protocols at the moment, 6rd and DS-Lite. Without a way to get this information from the ISP's DHCP server, there is no way to reliably use Mikrotik routers on many ISP connections.
RFC 5969 defines 6rd, a protocol based on 6to4. OPTION_6RD (212) for DHCPv4 provides the prefix, mask and length and the addresses of 6rd border relays to the client.
RFC 6333 defines DS-Lite, which uses an IPIPv6 tunnel to a remote CGNAT gateway (called AFTR) in order to move IPv4 through a native IPv6 network. RFC 6334 defines the corresponding OPTION_AFTR_NAME (64) for DHCPv6 to inform the client of the fully qualified domain name of the AFTR.
Ideally these protocols would be supported directly, but in the meantime they could be scripted, if the DHCP(v4/v6) client could be configured to request arbitrary options and provide the returned values to a script. Please add that functionality to the DHCP clients in RouterOS.