(Isn’t this a bikeshedding sort of question?)
Simple answer: blank is fine. This way, it presents no distraction or slowdown for end-users and spares people who want a blank start page from having to customise it to get it that way.
Any end-users who want something specific can customise their own browser to their own particular requirements. Please don’t force those preferences on all new users.
Also, keeping that page blank by default avoids wasting Purism staff time on something that is unimportant relative to Purism’s goals. Please, focus on the hardware and firmware, which is Purism’s USP. Thank you.