thanks for opening this up - I think it is great to raise the issue of ICT & Knowledge management in the early stage of platform development.
First of all, I think it is critical to define who the target users of this platform will be. They are the one who we expect will be engaging with it and ultimately make it grow and flourish. The more we know about them, the better we will be able to build a platform responding to their information and knowledge needs through the information and communication channels they already use.
To "ensure that knowledge products and other platform contents are used, useful, adopted and upscaled" the first step is design knowledge products with the users - as stated by the principles for digital development adopted by various sister UN agencies, among others (e.g. UNICEF, UNDP, UNHCR, WHO).
There is indeed a huge difference in the information required and the ICT tools used by policy & decision makers, researchers, humanitarian operators, and vulnerable communities: this doesn't mean that the platform cannot serve more than one of these groups. By making the platform agile, as recommended by Joel, it will be easier to add/remove modules dynamically.
Another possible idea is to channel some of the interaction on external platforms that target user groups may be already using. If the Platform will be hosted in-house, it will provide the chance to have only verified information and knowledge products on the platform while leaving the community freely able to share knowledge outside. With ad hoc facilitation, the knowledge generated in this community could also feed the platform itself after validation. For the more, if the community is hosted on a platform included in zero-rating packages (such as that offered by Facebook in many countries of the developing world) this would allow having knowledge available for free to a larger user base.
I definitely agree with the point made by Andrew Nadeau. Especially if Sub-Saharan Africa is a major target of this platform, it is clear that we should make it mobile-friendly. Mobile is the present and future of the region. Out of the existing 400’000, 60% of African villages already have access to mobile network coverage (Orange Telecom). For the more, the percentage of the population using the Internet is rising thanks to the growth of mobile broadband subscriptions (17.4% of population in 2015). Since 2013 it is more likely to find Internet access in an African households than a computer.
I also think it is good to think about the features this Platform may have.
No matter who the users will be - I am positive that they will be hungry for information, knowledge and training. Learning tools, as recommended by Fabiana, are a great way to engage users. They can also be instrumental in attracting users to the platform - especially if training courses provide participants with simple certificates. Monitoring the way people does tests would also provide with relevant information about the knowledge gaps of key stakeholders.
Finally, I think that investing into facilitation to provide the users with access to information and the tools on the platform will be critical. Should I choose between investing more in technology or facilitation I won't have any doubts: facilitation can transform the platform into a community, the other way around is unlikely to happen.
Hope it helps for now!