I can only think of two weak areas.
Weight of the bike, and cams.
The bike was designed to handle any stress expected from World Superbike racing, so it's overbuilt for average street use. But then that's a positive point for me.
You can substitute parts to lighten the bike, but it'll never be as light as today's I-4's.
The engine uses spur gears to drive the cams, and all those gears are heavier than belts or chains, but they are totally reliable and accurate. And I consider that a huge plus.
About the only real weak point of the whole bike is the cams.
They are cast nodular iron as opposed to steel as in the RC30.
If you weld and re-grind them for higher lift and duration, they are known to crack in two.
The only way around that is to replace with billet cams, and they cost a fortune, if you can find them at all.
Otherwise the engine is incredibly durable and reliable and will last practically forever with routine mainteance.
My bike is going on 7 years old with almost 40K miles with no issues.