With the age difference, it's a terrible idea. Even Otto knew it would never work. The plan was just to force Rhaenyra to stay a virgin for long enough that she gets desperate enough to lose her maidenhead to someone and then Otto has grounds to disinherit her which is pretty much exactly what happened a few decades later with Daena The Defiant

In a hypothetical scenario where they were born close enough in age to make a marriage between them more appropriate (at least in a Targaryen incesty way) it actually might have worked. Their personalities aren't actually that different and, if they were raised from childhood knowing they would be co-rulers and Viserys took an interest in making sure Aegon turned out at least passable, there's no reason things might not have worked out