DocBook 5 schedule, tool chains, etc?

After keeping loose tabs on DocBook for several years, I find
myself looking hard at (gasp) installing and trying it out.  I
see, however, that DocBook 5 is coming along Real Soon Now.

http://docbook.org/specs/wd-docbook-docbook-5.0a1.html says that
Version 5.0 is a complete rewrite, using Relax NG and tidying up
assorted historical problems.  Sounds good to me, but then, I
don't have any legacy DocBook files to worry about :-).

Anyway, I'd like to know the most reasonable path for a DocBook
newby to follow at this point.  Like, how soon will 5.0 be in a
condition to be used?  What (Open Source) tool chains will be
available for it.  Like that...

I realize that the answers to these questions are unknown, but
even negative answers (e.g., "V5 won't be available for at least
N years") can be useful.  So, tell me what you can.

-r
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