What are some unique engineering challenges in designing large, widebody aircraft that do not apply to regional/corporate jets?
Technically, designing and manufacturing narrow-bodies does not differ much from designing wide-bodies. Sure, the scale is different, heavier jet engines, larger factories etc, but in principle the engineering issues to be solved are pretty much the same. Airbus' first design, the A300, was a wide-body. Sure, Embraer and others can utilise their experience for designing and manufacturing wide-bodies.

The real challenge is in the size of the market, and in conquering market share. Only Boeing and Airbus make successful wide-body aircraft. The combined deliveries per year for wide-bodies are a bit over 200 for all types, for narrow-bodies over 1,000, gearing up for > 1,100 in a couple of years.

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Industrial issues to be tackled for starting a wide-body plant:


The investment for designing and starting a manufacturing plant are higher: harder to secure capital.
The market size is smaller: securing a number of unit sales equates to conquering a more sizeable portion of the market than with narrow-bodies.
There are two well-established manufacturers with multiple types each, in multiple variations, cornering all segments of the market.


Very hard to compete here. Much better to scale up the regionals into the narrow-body sector, like China did with the C-919.