HTML is designed to serve a purpose that can last a long time.   The evolution of HTML was fairly reasonable up through HTML 4.01 and CSS 2, with only sensible levels of extension to the standard.   Then came the "Living Standard" of HTML 5 and the rapid feature bloat it embodies.

Do to the nature of HTML as a medium for sharing documents over long periods of time, any extensions to the standard should be made with great deliberation and consideration.   Care should be taken to assure that anything new actually adds function that is not easily available in the existing standard and it is a function that is important enough to cause loss of use to some people.   Anything redacted from the existing standard (or otherwise deprecated) should be done even more carefully so as to minimize what may be broken in so doing.

When adding to the standard great care should be not only in assuring good reason to add it, though also in assuring the way it is defined is fairly simple to implement in existing browsers.   That is think about how it integrates into the existing DOM structure for the common means of internally representing DOM (including a literal double DOM Tree representation).

Furthermore HTML, DOM, and CSS are parts of the same, always have been, though other things, such as scripting languages for use with HTML and CSS, should be separate.   That is to say that the standard should not require a particular scripting language be uses, and should not effect that language (like HTML5 disobeys this in its inclusion of JavaScript (AKA ECMAScript)).   It is alright to recommend the use of a given scripting language, though only recommend it and keep the standard to a separate organization.   Most use of scripting is not in the nature of ongoing usefulness, leaning more toward doing too much with a web page, so it need not be in the core standards.

Put simply the reasonable additions are those improvements that add to the usability of the standard in ways that were not already easily accomplished within the standard.   The second area is that each addition should fulfill a real need that can not be accomplished easily within the existing standard.   In HTML this means that a lot of what was added to HTML5 above and beyond HTML 4.01 is not reasonable, as it does not add any value, or only adds value that is already easily available in HTML 4.01.   Also a living standard does not work, in order to be a standard that can be fulfilled it must be a static standard.

After taking a good deal of time studying exactly what has been added to HTML 4.01 to create HTML5 so far, I feel that the reasonable additions are:

• Canvas, an area of explicit size to draw into by whatever scripts may be used.   Of some utility in some reasonable Web Pages, though also can be abused (nothing new on the ability to abuse).
• Standardizing Graphics file formats across systems.   Helps with information interchange.
• Kind of: Standardizing formats for streaming video.   This probably should be separate from web standards, though unfortunately many video streaming services use a web interface that embeds the video player.   Other protocols are better suited to this application.
• Defining point sizes for font size specifications (though NOT web fonts).
• Site Icons, definitely useful to aid in identification of site in browsers and bookmarks/hotlists.   This is a valid user helpful addition.

There is the debate as to how useful the video stream formats (codecs) chosen are a good fit for universal information usage.   That though is one that I speak about elsewhere.