Trying not to duplicate too much what Will has already said:
> 1) tools for character manipulation (index - find a substring in a string; scan - get substring from string; and so forth). It has always seemed the height of irony that a system dedicated to working with text cannot manipulate text in any convenient manner
This is one that is definitely on the "to do" list. The current team are
already working on several things, and new items tend to get written as
we need them. So this will happen at "some point" but it's not currently
clear when. Of course, there is nothing stopping other people writing a
module and asking for it to be included (after I guess a bit of reviewing).
> 2) some better looping or array mechanism
> 3) some better storage mechanism, so that a rudimentary database can be constructed. I have done this in newlfm, but it should be a bit easier.
Again, something like this is on my "list", at least. We have some
looping and data structuring code, but at the moment nothing for
databases. As Will points out, I suspect datatool will provide some
inspiration. Once again, feel free to write something now and ask for it
to get added. I'd hope that the team as a whole are keen for as many
people as possible to contribute (as with LaTeX2e, but in perhaps a more
structured way: hopefully we can have modules that cover things
systematically and so don't need several similar ones).
> 4) some better mid-document margin control, so that margins can change by user choice. Several have told me that this is not possible, but I have hacked the output routine and am quite clear that it is.
Once xparse and template are "done", the next thing to consider is page
layout and output routine, I think. So this will come up, I suppose,
there. Hopefully we will be able to complete the template discussions in
weeks rather than months, so it should not be so long.