I believe your ABAP skills would be well complemented by adding Archiving.
Archiving is a common need. Some installations / their managers may not realise it till they reach a critical stage. But it is definitely required to store away and remove from the transactional databased the old data which is not much used. This improves response times. However this also necessitates a transaction to bring back archived data on demand. I have seen programs doing this.
Hence Archiving/restoring is a good skill to acquire.
A couple of further additions I have seen suggested for technically interested persons are
MDM – Master Data Management,
You may also seek a couple of opinions and then decide for yourself. Also you may need to concentrate on one or two at a time, so that your efforts are well spent.
All the best!