This is my first time with the customisation system and I quite liked it! It’s a nice touch having an editor that is smart when it comes to things like tabs/spacing, closing brackets and even a nifty find feature 
There are two things I missed from other software though.
The first one isn’t that big of an issue - the facility to create an overall style that has all related customisations under it so that it can be backed up, ported to other installs via one file etc. We can make do without it, but it would be one of those nice to have things.
What would be really nice is having a simple way to edit templates. For example I might want to show some user info in the posts, such as user location, post count, or some other field from their profile. I vaguely remember seeing that it’s possible to make such edits via plug-ins, but it seems like an easier templating solution could be advantageous - especially in encouraging designers to make more elaborate designs and layouts.
Apart from that I continue to be impressed by Discourse, and we’ve had some nice comments about the forum already 
If you’re curious, the forum is about Elixir and you can find it here: