What are some current things that are lacking in Bitcoin core? Or am I better off making something else for the ecosystem?
That depends on your interests.
Many of the highest priority tasks in Bitcoin Core are rather complicated, unfortunately, even for people with experience. You can consult the issue tracker to get a feel for it.
Alternatively, there are lots of wallet apps out there and plenty of more straightforward projects on them. However they may have less of a research flavour.