An interesting approach to provide a framework. It sounds like you are building this SDK to be similar to the ref wallet, in that it is a general purpose SDK for use by any application (i.e. trading, saving [think portfolio], investing, recurring payments...), and by any particular target audience.
This will allow you to avoid dealing with market research or identification of a target audience, leaving those concerns to those who use the SDK to build a wallet with UI / UX tailored to specific needs. That is something we have needed from the start, so very glad to see this.
I like this proposal better than the one to produce only a UI / UX design but no code. The cost is also more favorable.