Can't promise on a new release at the moment as I've been having a bit
of trouble with my visa/starting my 1st job; and the dates for that
are still not finalized. I have started work on the new version;
though. I've just been working on really base level stuff at the
moment; a general wrapper for custom post types, syntactic sugar for
adding hooks, easier admin pages, a generalized configuration creator,
etc.
You'll have to check out how capabilities are mapped in custom post
types, and modify that filter accordingly. Justin Tadlock's post [1]
might be a good starting point, followed by reading the actual code in
WP implementing that.
Regarding the child types -- there is nothing in WP that makes sure
that post descendants are of a certain type. You'll have to modify a
lot of code to carry this out -- for custom types of child posts based
on the category of the parent post. I don't think this will be
possible without modifying EventPress code directly, though.
Your best bet would be to see how registration works at the moment,
and duplicate and split the code at that point itself, forking into
two paths based on the category. You can generalize that, if required
into mapping multiple categories to multiple post types if you think
that would be required at some other point.
A slight warning, though: the next version of EP is going to be a
complete rewrite from the ground up, whenever it is released.
Kunal
[1] http://justintadlock.com/archives/2010/07/10/meta-capabilities-for-custom-post-types