std.xml: Why is it so slow? Is there anything else wrong with it?

[dsimcha]

There seems to be a consensus around here that Phobos needs a good XML 
module, and that std.xml doesn't cut it, at least partly due to 
performance issues.  I have no clue how to write a good XML module from 
scratch.  It seems like noone else is taking up the project either. 
This leads me to two questions:

1.  Has anyone ever sat down and tried to figure out **why** std.xml is 
so slow?  Seriously, if noone's bothered to profile it or read the code 
carefully, then for all we know there might be some low hanging fruit 
and it might be an afternoon of optimization away from being reasonably 
fast.  Basically every experience I've ever had suggests that, if a 
piece of code has not already been profiled and heavily optimized, at 
least a 5-fold speedup can almost always be obtained just by optimizing 
the low-hanging fruit.  (For example, see my recent pull request for the 
D garbage collector.  BTW, if excessive allocations are a contributing 
factor, then fixing the GC should help with XML, too.)

If the answer is no, this hasn't been done, please post some canned 
benchmarks and maybe I'll take a crack at it.

2.  What other major defects/design flaws, if any, does std.xml have?

In other words, how are we really so sure that we need to start from 
scratch?