My initial reaction is just that the "user interface presentation" split feels unnatural. Almost every other working area requires real input from the "user interface" side. Just to pick a single example for each:
* Content Format -- what should the UI for "editing templates" look like? (T114454) * Content access & APIs -- what parts of our UI should be "baked in" to our content APIs? (ie, default thumbnail size? stub article cutoffs?) * Collaboration -- the UX is at least half the task here (T112984) * Software engineering -- Integrating CSS-preprocessing and templating mechanisms, say.
The process at [[mw:Wikimedia_Developer_Summit_2016/Scope#Working_Areas]] states, "We may end up having Phab projects for each of these working areas, assigning each WikiDev '16 proposal to one primary area. For some proposals, it may be good to put them in multiple projects, but let's try to resist that urge."
That's probably a good idea for most of the working groups, but it may be wise to be more accommodating with "user interface presentation". We'd want to ensure that we have adequate "design and UX" representation on all the proposals which could possibly need it. --scott