Wordpress takes in whatever you put into the edit screen. It could be z-m-l

for all wordpress cares. Then it's up to you to provide software to produce

what you want it to display in a web page or other output format. 

But if you retrieve it for purposes of editing again, it's still whatever you put

in. Maybe z-m-l.

I ;put in html because that's what dp/pg provides that looks halfway decent

in its native form and includes pictures. You know as well as I that I'd be

much happier if it were otherwise. But I'm dealing with what's available

in the way of publishable text (whatever format) and systems capable

of supporting what DP does, without making preconditions about what

the text format or the data storage technique might be. So far I haven't

found much in the way of lightweight marked up text to work with.

So as far as a system which includes the ability to store work, share it,

retrieve it, edit it, put it back, and assemble it into various output formats 

with more or less difficulty, then wp is on my list. It doesn't require

html; it accepts html. Probably more people use wp than any other

system I can think of for handling etexts other than email, and there isn't

much in the ay of ebook fodder in email format that I've seen so far. It's

done a pretty good job so far keeping out the spammers, bots, and

hackers so far, which is something I'd prefer not to spend my time on.

Apparently it's not on your list because it stores text in a database. 

For me it's unpleasant, but I'll work with it. It's implementation choices 

are better or worse than others, including how it stores text, what the 

default editors are, and what the standard input and output formats 

are. Suggest some other platforms and maybe I'll add them to  my list. The

only ones that come to mind right now are DP, wordpress (and maybe other

blog engines).and wiki software, inculding TIA and its kin. What do you 

recommend for a platform?