A JSON file containing all the HTML5 entities is now available at http://dev.w3.org/html5/spec/entities.json.
I tested from the interpreter to see if it matches the values in html.entities.html5 and there are a dozen of entities that need to be updated:

>>> s = json.load(open('entities.json'))
>>> from html.entities import html5
>>> for (k1,i1),(k2,i2) in zip(sorted(s.items()), sorted(html5.items())):
...   if i1['characters'] != i2: (k1, k2, i1['characters'], i2, i1['codepoints'], list(map(ord, i2)))
... 
('⃜', 'DotDot;', '⃜', '◌⃜', [8412], [9676, 8412])
('̑', 'DownBreve;', '̑', '◌̑', [785], [9676, 785])
('⟨', 'LeftAngleBracket;', '⟨', '〈', [10216], [9001])
('
', 'NewLine;', '\n', '␊', [10], [9226])
('⟩', 'RightAngleBracket;', '⟩', '〉', [10217], [9002])
('	', 'Tab;', '\t', '␉', [9], [9225])
('⃛', 'TripleDot;', '⃛', '◌⃛', [8411], [9676, 8411])
('⟨', 'lang;', '⟨', '〈', [10216], [9001])
('⟨', 'langle;', '⟨', '〈', [10216], [9001])
('⟩', 'rang;', '⟩', '〉', [10217], [9002])
('⟩', 'rangle;', '⟩', '〉', [10217], [9002])
('⃛', 'tdot;', '⃛', '◌⃛', [8411], [9676, 8411])

The Tools/scripts/parseentities.py script should also be updated (or possibly a new, separate script should be added), so it can be used to generate the html5 dict.  I'm setting this as release blocker so that the update gets done before the release (other values might change in the meanwhile).

I say replace the code.  HTML 4.01 won’t be updated.

I think it's ok to have a separate file rather than patching the existing one (see attached patch).  If the old script is not used anymore it could be removed, otherwise we could just leave it there.

Version with --patch to modify Lib/html/entities.py automatically

New changeset dd8b969d7459 by Ezio Melotti in branch 'default':
#16245: add a script to generate the html.entities.html5 dict.
http://hg.python.org/cpython/rev/dd8b969d7459

New changeset 1eb1c6942ac8 by Ezio Melotti in branch '3.3':
#16245: Fix the value of a few entities in html.entities.html5.
http://hg.python.org/cpython/rev/1eb1c6942ac8

New changeset 70fab10cd542 by Ezio Melotti in branch 'default':
#16245: merge with 3.3.
http://hg.python.org/cpython/rev/70fab10cd542

New changeset fb80df16c4ff by Ezio Melotti in branch 'default':
Add Misc/NEWS entry for dd8b969d7459/#16245.
http://hg.python.org/cpython/rev/fb80df16c4ff

I now committed an improved version of the script (thanks Iuliia!) and updated the html.entities.html5 dictionary accordingly.

I'm leaving this open because we will have to check if the dictionary is still updated before the release of Python 3.4.

Shouldn't this be deferred blocker?