It makes sense to release lower end units like X3 before a full MD4 from system 6000. Consumers may buy the X3 then buy again when/if system 6000 MD4 is released. Would be less likely if MD4 was released first for the consumer to buy a version with lesser features. I sometimes use my MD3 in a working Poco but wouldn't want to replace it with a native md3. There are too many effective alternatives with more flexiblity.