In 1890 the Germans and British sorted out their colonial claims in East Africa, with the Germans conceding on a few more disputed areas (Zanzibar, Wituland and Uganda) than Britain, in exchange for British cession of Helgoland to Germany.
What if a the two countries made a more thorough-going territorial exchange at this time. For instance, by trading German Tanganyika for British Nigeria, to allow the British to have their Cape-to-Cairo Route while making the German bloc in west Africa (Kamerun and Nigeria) match the French bloc in strength?
Extending this further, what about Gold Coast to Germany in exchange for Southwest Africa to Britain? That gives Germany a more productive colony with closer shipping routes to Germany, revives historic German involvement in the area (there was a Prussian Gold Coast), improves the defensive depth of Togoland, while at the same time for the British gaining southwest Africa provides more defensive depth for the Cape Colony and a more dominating position surrounding the Boer Republics?
If not then, perhaps the opportunity might emerge later. What if the Germans, instead of ham-handedly testing the Anglo-French Entente Cordiale with its loud opposition to France in Morrocco, instead offered a colonial arrangement with the British to compete with France in having amicable colonial relations with London, in 1904-1905. At this time, Britain probably values securing the hinterland around South Africa, and the ability to establish a Cape-to-Cairo route even more, so a German offer to exchange all or part of Tanganyika and Southwest Africa for all or part of Nigeria and/or the Gold Coast or territories elswhere (the Gilberts and Phoenix islands?) could be hard for London to resist.
Another time at which an expanded Anglo-German deal might be opportune
would be in 1893-1894, in the near-term aftermath of the Franco-
Russian dual alliance. A colonial deal might offer London and Berlin
an opportunity for a diplomatic countermove with continental and
balance of power implications as well the more concrete possibilities
of colonial consolidation.