Marvel/Disney was very shrewd in choosing to release Captain America: The Winter Soldier
in April instead during the much more crowded summer months. Other films have reached blockbuster status by releasing in late winter/spring when there is less competition. Although CA is facing a real contender in Denzel Washington's The Equalizer
* in its second weekend, I think that it stands a great chance of opening big and then holding on for a less than 60% drop.
Domestically, TWS could make $250 million or more if it is well received by the public and has the sort of marketing behind it that IM3 has had. In the overseas market it could easily do $400 million+ since TFA took in a better than expected $191M OS. With a boost from TA, Marvel's Chinese marketing partnership and the inclusion of Jackson, Johansson and Redford, this could break out in a big way. My prediction is $650M WW but I rounded up to $700M. In for a penny, in for a pound, right?
* The Equalizer is a remake of the TV show from the 1980s that featured Edward Woodward as a mercenary who switched to protecting ordinary people who were being victimized by criminals. The production has been in some turmoil as the first director suddenly dropped it and filming was postponed. I haven't heard what the status is since then.