Perhaps it's a good point in time to summarise the pros & cons of the issue:
(a) Fixed toolbar (where the formatting buttons are) - easier formatting.
(b) Auto-expanding text area - apparently more suitable for mobile device users where multiple scrollbars may be problematic.
(c) One single scrollbar (the browser's) - apparently good for mobile users and/or to streamline the general interface.
(1) Floating 'Publish' panel on right-hand side - makes for substantially more scrolling during writing/editing to access 'Save' button, &c, especially for long posts.
(2) Other floating righthand-side panels ('Tags,' 'Categories,' &c) - again leading to extra scrolling to access them for tagging and categorising.
(3) Auto-expanding text area - less practical (or impractical) for non-mobile users, especially with respect to the floating 'Publish,' 'Tag,' &c panels (point 2 above).
(4) Lack of 'Save' button in the editing toolbar - especially in view of the floating 'Publish' & related panels on the right-hand side. It is good computing practice to save the work regularly & frequently, and the floating panels detract from this.
(5) One scrollbar - relying on the environmental scrollbar to do the work of two separate functions is not good computing practice anyway. Desktop/laptop computers are main computers & these are to provide higher functionality than mobile devices. The environmental functions of the browser works UNTIL the browser itself has issues (non-updates, &c).
(6) No opt-out choice for new interface, especially with regard to users who blog mainly on main computers rather than mobile devices.
Other apparent/alleged issues (related or unrelated to the new interface) mentioned in this thread or other threads (or now noticed during use):
(7) Stripping of codes when pasting from other applications (e.g. WordPad, YouTube, &c) in either visual or text mode.
(8) Noticeable reduction in fount size of text in the editing text box to varying degrees depending on your theme.
(9) Alleged wordcount problems for posts as mentioned in some other threads, which I couldn't confirm or deny as of yet.
(10) Cannot flush-centre paired images side by side, which may be an issue for some users on some themes.
(A) Pin (make stationary) the Publish, Tag, &c, panels to make their buttons more effectually accessible.
(B) If not (A) above, then introduce a 'Save' button in the editing toolbar to make saving an less tedious exercise. Mobile users (like my wife!) will appreciate that greatly.
The above two actions are easily doable, by virtue of the fact that the more difficult auto-expanding text area and internal scrollbar removal have already been done.
Commenters please advise if I've summarised the issues right. Thanks to all.