Core has to have some useless feature every release, this is the useless feature of 4.5 :(, This feature is designed with the best practices of 2010 instead of 2016. There is no way to add a retina enhanced versions of the logo and no way to add "mobile" version, so this feature is not "responsive" nor retina friendly by design.

To add insult to injury, a major aspect of having a logo is its placement which in the real life have to take into account the other elements of the page and you can not just place it at top left corner and hope for the best. There is no placement support in this feature.

It is totally possible that only 1% of the users care about what I said above, and the feature will turn out to be a huge success, but the proper development here, since there is no real feedback about how the feature is being used in jetpack, is to first push it only into the default themes to get the feedback and after that decide if it is core worthy. This feature could have waited for 4.6, their is no reason to rush it into 4.5.

As for discoverability, this is a two edged sword. If the feature is a "theme optional" thing, why would people assume it is at the costumizer at all, but once it is in core and every new user learns where it is from the default themes, every theme that do not implement it will get support questions of the type "I have a bug, I went to change the site logo but the thing is not there". The theme review team might as well add it as a requirement.

sorry for the long rant. This is absolutely the last core ticket I am getting involved with so I am hoping that all future rants will be only half fact based as true comment on the internet are supposed to be.