I agree and I'd even move the Stream and WooCommerce dropins out of core as well. Without a proper Dropins delivery system as we are starting to build in MD5.2.1, the easiest way to promote those features is to just include them in core. They are lightweight and don't really make the theme much heavier, but I love that it would shave nearly 100kb of weight off the MD theme files.
This idea could even be expanded to the ESP (Aweber, Mailchimp, etc.) libraries and only import the ones needed per site. I have big ambitions for how pluggable MD will keep becoming but Dropin portability is a big priority around here.