Well lets be honest, Portugal's status as a great power ended with the independence of Brazil. That being said, I think that a Portugal under Pedro V had a good chance of retaining is second-tier status. He was a modern, liberal monarch who supported industry, so no doubt Pedro wouldn't interfere with politics as much as his mother, brother and nephew did. So long-term the Portuguese Monarchy could survive into the 20th and 20st centuries as a national symbol of unity, like the Bourbons of Spain and the British Royal House. And with a forward thinking and looking sovereign, we could see Portugal develop into an industrialized nation, similar to that of Britain.
However, the pink map would be incredibly difficult to pull of, mainly because Portugal was directly challenging British interests. Britain, if you remember, was Portugal's oldest and closest ally, and because of this the Portuguese had no backup when they challenged their old friend. That being said, I think that if they had colonized the region earlier, before the scramble for Africa, then it would have gone unchallenged. Sure Britain might demand the right to freely move across Portuguese territory and control of a railway, but other then that it is possible.