TextTrackCue contructor API change

After the recent changes to the HTML spec and the WebVTT spec where we've
made TextTrack and TextTrackCue more generic to deal with different types
of text track cue file formats, I have some concerns about backwards
compatibility.

Before the change, we had defined TextTrackCue as follow

enum AutoKeyword { "auto" };
[Constructor(double startTime, double endTime, DOMString text)]
interface TextTrackCue : EventTarget {
  readonly attribute TextTrack? track;

           attribute DOMString id;
           attribute double startTime;
           attribute double endTime;
           attribute boolean pauseOnExit;
           attribute DOMString vertical;
           attribute boolean snapToLines;
           attribute (long or AutoKeyword) line;
           attribute long position;
           attribute long size;
           attribute DOMString align;
           attribute DOMString text;
  DocumentFragment getCueAsHTML();

           attribute EventHandler onenter;
           attribute EventHandler onexit;
};

Now, after the change, it is:

interface TextTrackCue : EventTarget {
  readonly attribute TextTrack? track;

           attribute DOMString id;
           attribute double startTime;
           attribute double endTime;
           attribute boolean pauseOnExit;

           attribute EventHandler onenter;
           attribute EventHandler onexit;
};

This means in particular that the TextTrackCue() constructor does not exist
any longer and a TextTrackCue cannot be instantiated any more, but only its
derived interface such as WebVTTCue() can.

I am concerned because the major browsers have implemented the
TextTrackCue() constructor already [1] (actually: I am not sure what
Firefox is doing, because they are implementing this right now.).  The
TextTrackCue() constructor basically created WebVTT cues and people are
already using TextTrackCue() to create WebVTT cues programmatically [2].

Is this a problem that we should deal with or should we just deprecate the
TextTrackCue() constructor?

I know this is likely a question for the HTML WG and the WHATWG, but since
people on this list are likely to have used the TextTrackCue() constructor
before, I wonder what their thoughts about it are.

Cheers,
Silvia.

[1]
http://compatibility.shwups-cms.ch/de/home/?&property=TextTrackCue.prototype
[2] http://code.ohloh.net/search?s="TextTrackCue"