In reply to kris.

sitemaps /caching / lazy image loading / upload image optimisation / basic contact form – should be IMHO built in

Shhhhh, all those features built in would hurt marketshare of very important plugins like Jetpack https://jetpack.com/support/features/ and their upselling plans and also the wordpress.com account leads from Jetpack would drop like a rock. Also it would be more difficult for Jetpack and wordpress.com to charge extra for SEO etc.