Questions about text properties

[Garreau\, Alexandre]

I was reading the text properties and overlays manual part and I’ve some
questions about them:
– why is everything using plists rather than alist? if I’m right plists
  are just like alist but more conveniently displayed as sexps (hence
  used for keyword arguments) and not overridable by appending: however
  having a lot of common text properties between part of text makes me
  wonder if sharing properties in memory wouldn’t have been relevant, it
  also would have made inheritance easier;
– how about adding stuff to a *value* of property, be it a list, or
  anything that could inherit, such as an alist, a keymap, etc.? it
  seems there are no functions for that;
— why does stuff everywhere (e.g. org-mode) appears to just bind RET,
  C-c C-c, mouse events, etc. to contextual do-everything functions,
  rather than only bind these on fontified parts of buffer, so not to
  have such meaningless hard to debug, read, and understand functions;
– why are properties rear-sticky by default rather than the opposite?
  why are stickiness properties biased toward this choice? that seems to
  reflect high confidence toward a such default;
– why is there only a mouse-face property, rather than a hover, click,
  pressed, active, focus, etc. (like in html/css) that would help
  distinguishing point, mouse, region, etc.? that feels rather limited;
– why can it only affects face rather than other properties so that to
  extend its behavior?
– sometimes most text properties can take a hook (that will be called
  lazily to compute a valid value), sometimes not (like for a display
  prop space);
— is the recenter thing about overlays related to the fact buffers are
  implemented with a buffer gap, or is it just something similar to
  fasten stuff?