I’m not so sure about moving tags to the top. They are an optional feature, and many users don’t use them at all. For those that do use tags, if we consider the initial input stage, I wonder which order the majority of users would consider more logical - inputting content and then tagging it, or vice versa? The current approach mirrors things like Twitter where the tags tend to come at the end.
But ultimately what matters is what the majority of users think, not what I think 
If we do consider changing this without an option to keep the tags on the bottom though, the ratio of people preferring on-top vs on-bottom will need to be pretty high, as I’m sure there will be people complaining that things have moved.
Regarding the deck/notetype selectors: icons are more compact, but do make support a bit harder. “Click the Cards… button” becomes “click the icon with the square brackets inside it at the top”. There’s currently no distinction between the icons associated with the two dropdowns, and the icons that modify the active dropdown. Maybe some alternatives we could use there are to embed the cards/fields icons inside the white square like is done with the field labels, and/or we could switch them to a hamburger menu.