Batak script became supported by Unicode, the Batak languages became technically ready for the 21th century. Practically there is still a long way to go because there is no font yet that supports Batak.
The cost of having a technically correct font that does justice to the language created is relatively minor; for some EUR 5000,- such a font will be created and become available under a free license.
Once a font is available, it is possible to reach out to museums in the Netherlands like the Tropenmuseum and ask them for quality scans of their documents in the Batak script. When these are then transcribed, a rich source of information about the Batak culture will become available.
There are plans for a conference in Bali where people who are involved in Indonesian languages are to be motivated for involvement in WMF projects. Demonstrating how languages can get a new lease of live can be done by having a source project running for the Batak languages in combination with Dutch museums.
This kind of outreach has been suggested to Wikimedia Australia. Sadly they have not come to a conclusion yet on what to do. I would love to see this project started as soon as possible and am happy to reach out to the Dutch museums.