If you plan to develop a BUS-POWERED device with 5V 4 A power requirement, and expect it to run from legacy USB ports (which are still something like 95% of all USB hosts) and using standard legacy cables, this would be a bad business proposition. First, most legacy (Type-A and uAB) ports have connectors with rating under 1.8 - 1.5 A. Then, most legacy cables are designed for 0.5 A ampacity. So your device won't fly.
If you are thinking if a regular hub can solve this problem, even if it is self powered with 12V-4.5A supply, it could accidentally have ganged power and supply more current, but the limitations are the same - connectors and old cables were not designed to carry 4 A load. So your device might work with this particular hub, but not with 90% of other hubs.
The 5V@4A power is, however, within basic specifications for the newer Type-C connector. Full-featured Type-C - Type-C cables must be able to carry up to 5A at 5V without delving into Power Delivery Protocol (elevated voltage allows to deliver more power). However, all 5-A cables must have an "electronic marker" (a special IC embedded into cable's overmold), and Type-C port controllers at both ends of Type-C link should refuse to supply any power if the marker is not found.
As one can imagine, all these special PD and marker protocols increase the cost of power links and ports, and substantially, and technically are quite beyond capabilities of a typical DIY person. So in this particular case you should abandon the idea to have your device to be bus powered, and resort to a wall AC-DC adapter with proper power rating (there are plenty of 5V4A wallwarts used for hubs). Or you need to re-design or re-think power specifications for your device using less power-hungry processors.