I don't know what's wrong with mikrotik their ospf doesn't work well with huawei or VyOS at times.
The new OSPF is a complete rewrite.
I would like to see IS-IS too eventually but a properly working OSPF is more important to me. Especially OSPFv3 on RouterOS v6 really does not work properly.
If they try to release too many new features day one on RouterOS v7 it will never stabilize. I wouldn't want them to delay ROS 7 release just to add IS-IS (and hopefully they wouldn't).